set up config_accessor with a default value by block

* ActiveSupport::Configurable should allow config_accessor to take
  default value by block, just like cattr_accessor.

    class User
      include ActiveSupport::Configurable
      config_accessor :hair_colors do
        [:brown, :black, :blonde, :red]
      end
    end

    User.hair_colors # => [:brown, :black, :blonde, :red]

* remove trailing whitespaces in configurable.rb and its test file.

* Update ActiveSupport CHANGELOG.

1 files changed, 13 insertions, 0 deletions

diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index c10a0b390b..59e112e3f9 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,5 +1,18 @@
 ## Rails 4.0.0 (unreleased) ##
 
+*   An optional block can be passed to `config_accessor` to set its default value
+
+        class User
+          include ActiveSupport::Configurable
+          config_accessor :hair_colors do
+            [:brown, :black, :blonde, :red]
+          end
+        end
+
+        User.hair_colors # => [:brown, :black, :blonde, :red]
+
+    *Larry Lv*
+
 *   ActiveSupport::Benchmarkable#silence has been deprecated due to its lack of
     thread safety. It will be removed without replacement in Rails 4.1. *Steve
     Klabnik*