Create 4.2 release notes guide scaffold [ci skip]

Point to future 4-2-stable branch for detailed changes. [ci skip]

Sync Active Support changelogs with release notes [ci skip]

4.2 Release Notes is a work in progress [ci skip]

Assorted fixes for AS release notes [ci skip]

* `Hash#deep_transform_keys` has already been backported
* Mentioning `ActiveSupport::SafeBuffer#prepend` in the "Deprecations" section would be enough
* Fix syntax in `Kernel#concern` example

Sync AS release notes with the latest commits [ci skip]

Synced 4.2 release notes with commits in railties [ci skip]

Sync AP Deprecations and Notable changes from CHANGELOG [ci skip]

Removed 4.2 release notes from the index [ci skip]

This deprecation was reverted in 489a8f2 [ci skip]

Synced Active Record changelogs for 4.2 release notes [ci skip]

Synced Active Model changelog with the release notes [ci skip]

Added cc26b6b as a 'Removal' item in AP release notes [ci skip]

Use 'character' instead of 'symbol' to avoid confusion [ci skip]

Edit pass on 4.2 release notes [ci skip]

:memo: :lipstick: Use `.xyz` and `#xyz` appropiately [ci skip]

2 files changed, 249 insertions, 0 deletions

diff --git a/guides/source/4_2_release_notes.md b/guides/source/4_2_release_notes.md
new file mode 100644
index 0000000000..7782b900ad
--- /dev/null
+++ b/guides/source/4_2_release_notes.md
@@ -0,0 +1,243 @@
+Ruby on Rails 4.2 Release Notes
+===============================
+
+Highlights in Rails 4.2:
+
+These release notes cover only the major changes. To know about various bug
+fixes and changes, please refer to the change logs or check out the
+[list of commits](https://github.com/rails/rails/commits/master) in the main
+Rails repository on GitHub.
+
+--------------------------------------------------------------------------------
+
+Upgrading to Rails 4.2
+----------------------
+
+If you're upgrading an existing application, it's a great idea to have good test
+coverage before going in. You should also first upgrade to Rails 4.1 in case you
+haven't and make sure your application still runs as expected before attempting
+an update to Rails 4.2. A list of things to watch out for when upgrading is
+available in the
+[Upgrading Ruby on Rails](upgrading_ruby_on_rails.html#upgrading-from-rails-4-1-to-rails-4-2)
+guide.
+
+
+Major Features
+--------------
+
+
+
+Railties
+--------
+
+Please refer to the
+[Changelog](https://github.com/rails/rails/blob/4-2-stable/railties/CHANGELOG.md)
+for detailed changes.
+
+### Removals
+
+* The `rails application` command has been removed without replacement.
+  ([Pull Request](https://github.com/rails/rails/pull/11616))
+
+### Notable changes
+
+* Introduced `bin/setup` script to bootstrap an application.
+  ([Pull Request](https://github.com/rails/rails/pull/15189))
+
+* Changed default value for `config.assets.digest` to `true` in development.
+  ([Pull Request](https://github.com/rails/rails/pull/15155))
+
+* Introduced an API to register new extensions for `rake notes`.
+  ([Pull Request](https://github.com/rails/rails/pull/14379))
+
+* Introduced `Rails.gem_version` as a convenience method to return `Gem::Version.new(Rails.version)`.
+  ([Pull Request](https://github.com/rails/rails/pull/14101))
+
+
+Action Pack
+-----------
+
+Please refer to the
+[Changelog](https://github.com/rails/rails/blob/4-2-stable/actionpack/CHANGELOG.md)
+for detailed changes.
+
+### Removals
+
+* Removed support for setting the `to:` option of a router to a symbol or a
+  string that does not contain a `#` character:
+
+      get '/posts', to: MyRackApp    => (No change necessary)
+      get '/posts', to: 'post#index' => (No change necessary)
+      get '/posts', to: 'posts'      => get '/posts', controller: :posts
+      get '/posts', to: :index       => get '/posts', action: :index
+
+  ([Commit](https://github.com/rails/rails/commit/cc26b6b7bccf0eea2e2c1a9ebdcc9d30ca7390d9))
+
+### Notable changes
+
+* The `*_filter` family methods has been removed from the documentation. Their
+  usage are discouraged in favor of the `*_action` family methods:
+
+      after_filter          => after_action
+      append_after_filter   => append_after_action
+      append_around_filter  => append_around_action
+      append_before_filter  => append_before_action
+      around_filter         => around_action
+      before_filter         => before_action
+      prepend_after_filter  => prepend_after_action
+      prepend_around_filter => prepend_around_action
+      prepend_before_filter => prepend_before_action
+      skip_after_filter     => skip_after_action
+      skip_around_filter    => skip_around_action
+      skip_before_filter    => skip_before_action
+      skip_filter           => skip_action_callback
+
+  If your application is depending on these methods, you should use the
+  replacement `*_action` methods instead. These methods will be deprecated in
+  the future and eventually removed from Rails.
+  (Commit [1](https://github.com/rails/rails/commit/6c5f43bab8206747a8591435b2aa0ff7051ad3de),
+  [2](https://github.com/rails/rails/commit/489a8f2a44dc9cea09154ee1ee2557d1f037c7d4))
+
+* Added HTTP method `MKCALENDAR` from RFC-4791
+  ([Pull Request](https://github.com/rails/rails/pull/15121))
+
+* `*_fragment.action_controller` notifications now include the controller and action name
+  in the payload.
+  ([Pull Request](https://github.com/rails/rails/pull/14137))
+
+* Segments that are passed into URL helpers are now automatically escaped.
+  ([Commit](https://github.com/rails/rails/commit/5460591f0226a9d248b7b4f89186bd5553e7768f))
+
+* Improved Routing Error page with fuzzy matching for route search.
+  ([Pull Request](https://github.com/rails/rails/pull/14619))
+
+* Added option to disable logging of CSRF failures.
+  ([Pull Request](https://github.com/rails/rails/pull/14280))
+
+
+Action Mailer
+-------------
+
+Please refer to the
+[Changelog](https://github.com/rails/rails/blob/4-2-stable/actionmailer/CHANGELOG.md)
+for detailed changes.
+
+### Notable changes
+
+
+Active Record
+-------------
+
+Please refer to the
+[Changelog](https://github.com/rails/rails/blob/4-2-stable/activerecord/CHANGELOG.md)
+for detailed changes.
+
+### Deprecations
+
+* Deprecated using `.joins`, `.preload` and `.eager_load` with associations that
+  depends on the instance state (i.e. those defined with a scope that takes an
+  argument) without replacement.
+  ([Commit](https://github.com/rails/rails/commit/ed56e596a0467390011bc9d56d462539776adac1))
+
+* Deprecated passing Active Record objects to `.find` or `.exists?`. Call `#id`
+  on the objects first.
+  (Commit [1](https://github.com/rails/rails/commit/d92ae6ccca3bcfd73546d612efaea011270bd270),
+  [2](https://github.com/rails/rails/commit/d35f0033c7dec2b8d8b52058fb8db495d49596f7))
+
+* Deprecated half-baked support for PostgreSQL range values with excluding
+  beginnings. We currently map PostgreSQL ranges to Ruby ranges. This conversion
+  is not fully possible because the Ruby range does not support excluded
+  beginnings.
+
+  The current solution of incrementing the beginning is not correct and is now
+  deprecated. For subtypes where we don't know how to increment (e.g. `#succ`
+  is not defined) it will raise an `ArgumentError` for ranges with excluding
+  beginnings.
+
+  ([Commit](https://github.com/rails/rails/commit/91949e48cf41af9f3e4ffba3e5eecf9b0a08bfc3))
+
+### Notable changes
+
+* Added support for `#pretty_print` in `ActiveRecord::Base` objects.
+  ([Pull Request](https://github.com/rails/rails/pull/15172))
+
+* PostgreSQL and SQLite adapters no longer add a default limit of 255 characters
+  on string columns.
+  ([Pull Request](https://github.com/rails/rails/pull/14579))
+
+* `sqlite3:///some/path` now resolves to the absolute system path `/some/path`.
+  For relative paths, use `sqlite3:some/path` instead. (Previously, `sqlite3:///some/path`
+  resolved to the relative path `some/path`. This behaviour was deprecated on
+  Rails 4.1.)
+  ([Pull Request](https://github.com/rails/rails/pull/14569))
+
+* Introduced `#validate` as an alias for `#valid?`.
+  ([Pull Request](https://github.com/rails/rails/pull/14456))
+
+* `#touch` now accepts multiple attributes to be touched at once.
+  ([Pull Request](https://github.com/rails/rails/pull/14423))
+
+* Added support for fractional seconds for MySQL 5.6 and above.
+  (Pull Request [1](https://github.com/rails/rails/pull/8240), [2](https://github.com/rails/rails/pull/14359))
+
+* Added support for the `citext` column type in PostgreSQL adapter.
+  ([Pull Request](https://github.com/rails/rails/pull/12523))
+
+* Added support for user-created range types in PostgreSQL adapter.
+  ([Commit](https://github.com/rails/rails/commit/4cb47167e747e8f9dc12b0ddaf82bdb68c03e032))
+
+Active Model
+------------
+
+Please refer to the
+[Changelog](https://github.com/rails/rails/blob/4-2-stable/activemodel/CHANGELOG.md)
+for detailed changes.
+
+### Notable changes
+
+* Introduced `#validate` as an alias for `#valid?`.
+  ([Pull Request](https://github.com/rails/rails/pull/14456))
+
+
+Active Support
+--------------
+
+Please refer to the
+[Changelog](https://github.com/rails/rails/blob/4-2-stable/activesupport/CHANGELOG.md)
+for detailed changes.
+
+### Removals
+
+* Removed deprecated `Numeric#ago`, `Numeric#until`, `Numeric#since`,
+  `Numeric#from_now`. ([Commit](https://github.com/rails/rails/commit/f1eddea1e3f6faf93581c43651348f48b2b7d8bb))
+
+* Removed deprecated string based terminators for `ActiveSupport::Callbacks`.
+  ([Pull Request](https://github.com/rails/rails/pull/15100))
+
+### Deprecations
+
+* Deprecated `Class#superclass_delegating_accessor`, use `Class#class_attribute`
+  instead. ([Pull Request](https://github.com/rails/rails/pull/14271))
+
+* Deprecated `ActiveSupport::SafeBuffer#prepend!` as `ActiveSupport::SafeBuffer#prepend`
+  now performs the same function. ([Pull Request](https://github.com/rails/rails/pull/14529))
+
+### Notable changes
+
+* The `humanize` inflector helper now strips any leading underscores.
+  ([Commit](https://github.com/rails/rails/commit/daaa21bc7d20f2e4ff451637423a25ff2d5e75c7))
+
+* Added `SecureRandom::uuid_v3` and `SecureRandom::uuid_v5`.
+  ([Pull Request](https://github.com/rails/rails/pull/12016))
+
+* Introduce `Concern#class_methods` as an alternative to `module ClassMethods`,
+  as well as `Kernel#concern` to avoid the `module Foo; extend ActiveSupport::Concern; end`
+  boilerplate. ([Commit](https://github.com/rails/rails/commit/b16c36e688970df2f96f793a759365b248b582ad))
+
+Credits
+-------
+
+See the
+[full list of contributors to Rails](http://contributors.rubyonrails.org/) for
+the many people who spent many hours making Rails, the stable and robust
+framework it is. Kudos to all of them.
diff --git a/guides/source/upgrading_ruby_on_rails.md b/guides/source/upgrading_ruby_on_rails.md
index 03d1f2a3a0..6800e71a3c 100644
--- a/guides/source/upgrading_ruby_on_rails.md
+++ b/guides/source/upgrading_ruby_on_rails.md
@@ -22,6 +22,12 @@ Rails generally stays close to the latest released Ruby version when it's releas
 
 TIP: Ruby 1.8.7 p248 and p249 have marshaling bugs that crash Rails. Ruby Enterprise Edition has these fixed since the release of 1.8.7-2010.02. On the 1.9 front, Ruby 1.9.1 is not usable because it outright segfaults, so if you want to use 1.9.x, jump straight to 1.9.3 for smooth sailing.
 
+Upgrading from Rails 4.1 to Rails 4.2
+-------------------------------------
+
+NOTE: This section is a work in progress.
+
+
 Upgrading from Rails 4.0 to Rails 4.1
 -------------------------------------