Make `db:migrate:status` to render `1_some.rb` format migrate files.

`1_valid_people_have_last_names.rb` and
`20150823202140_create_users.rb` are valid migration file name.
But `1_valid_people_have_last_names.rb` is rendered as
`********** NO FILE **********` when `rake db:migrate:status`.

Fix to this bug, this commit includes

* define some API private methdos and a Constant
  `match_to_migration_filename?`, `parse_migration_filename`, and
  `MigrationFilenameRegexp`
* use these methods in `db:migrate:status` task

Example:

These files are in `db/migrate`

* 1_valid_people_have_last_names.rb
* 20150819202140_irreversible_migration.rb
* 20150823202140_add_admin_flag_to_users.rb
* 20150823202141_migration_tests.rb
* 2_we_need_reminders.rb
* 3_innocent_jointable.rb

we can migrate all of them.

Before

```shell
$ bundle exec rake db:migrate:status

...

 Status   Migration ID    Migration Name
--------------------------------------------------
   up     001             ********** NO FILE **********
   up     002             ********** NO FILE **********
   up     003             ********** NO FILE **********
   up     20150819202140  Irreversible migration
   up     20150823202140  Add admin flag to users
   up     20150823202141  Migration tests
```

After

```shell
$ bundle exec rake db:migrate:status

...

 Status   Migration ID    Migration Name
--------------------------------------------------
   up     001             Valid people have last names
   up     002             We need reminders
   up     003             Innocent jointable
   up     20150819202140  Irreversible migration
   up     20150823202140  Add admin flag to users
   up     20150823202141  Migration tests
```

1 files changed, 22 insertions, 0 deletions

diff --git a/railties/test/application/rake/migrations_test.rb b/railties/test/application/rake/migrations_test.rb
index 2d8bd7c571..6b74707959 100644
--- a/railties/test/application/rake/migrations_test.rb
+++ b/railties/test/application/rake/migrations_test.rb
@@ -154,6 +154,28 @@ module ApplicationTests
         end
       end
 
+      test 'running migrations with not timestamp head migration files' do
+        Dir.chdir(app_path) do
+
+          app_file "db/migrate/1_one_migration.rb", <<-MIGRATION
+            class OneMigration < ActiveRecord::Migration
+            end
+          MIGRATION
+
+          app_file "db/migrate/02_two_migration.rb", <<-MIGRATION
+            class TwoMigration < ActiveRecord::Migration
+            end
+          MIGRATION
+
+          `bin/rake db:migrate`
+
+           output = `bin/rake db:migrate:status`
+
+           assert_match(/up\s+001\s+One migration/, output)
+           assert_match(/up\s+002\s+Two migration/, output)
+        end
+      end
+
       test 'schema generation when dump_schema_after_migration is set' do
         add_to_config('config.active_record.dump_schema_after_migration = false')