synchronize changelogs and 4.1 release notes. [ci skip]

Conflicts:
	actionpack/CHANGELOG.md
	activerecord/CHANGELOG.md
	activesupport/CHANGELOG.md
	railties/CHANGELOG.md

guides/source/4_1_release_notes.md

@@ -291,6 +291,10 @@ for detailed changes.
   with `config.active_record.maintain_test_schema = false`. ([Pull
   Request](https://github.com/rails/rails/pull/13528))
 
+* Introduce `Rails.gem_version` as a convenience method to return
+  `Gem::Version.new(Rails.version)`, suggesting a more reliable way to perform
+  version comparison. ([Pull Request](https://github.com/rails/rails/pull/14103))
+
 
 Action Pack
 -----------
@@ -346,10 +350,14 @@ for detailed changes.
   params "deep munging" that was used to address security vulnerability
   CVE-2013-0155. ([Pull Request](https://github.com/rails/rails/pull/13188))
 
-* New config option `config.action_dispatch.cookies_serializer` for specifying
-  a serializer for the signed and encrypted cookie jars. (Pull Requests [1](https://github.com/rails/rails/pull/13692), [2](https://github.com/rails/rails/pull/13945) / [More Details](upgrading_ruby_on_rails.html#cookies-serializer))
+* New config option `config.action_dispatch.cookies_serializer` for specifying a
+  serializer for the signed and encrypted cookie jars. (Pull Requests
+  [1](https://github.com/rails/rails/pull/13692),
+  [2](https://github.com/rails/rails/pull/13945) /
+  [More Details](upgrading_ruby_on_rails.html#cookies-serializer))
 
-* Added `render :plain`, `render :html` and `render :body`. ([Pull Request](https://github.com/rails/rails/pull/14062) /
+* Added `render :plain`, `render :html` and `render
+  :body`. ([Pull Request](https://github.com/rails/rails/pull/14062) /
   [More Details](upgrading_ruby_on_rails.html#rendering-content-from-string))
 
 
@@ -705,7 +713,7 @@ for detailed changes.
   `available_locales`
   list. ([Pull Request](https://github.com/rails/rails/commit/8e21ae37ad9fef6b7393a84f9b5f2e18a831e49a))
 
-* Introduce Module#concerning: a natural, low-ceremony way to separate
+* Introduce `Module#concerning`: a natural, low-ceremony way to separate
   responsibilities within a
   class. ([Commit](https://github.com/rails/rails/commit/1eee0ca6de975b42524105a59e0521d18b38ab81))