Deprecate Rails::Plugin in favor of gems

Author: spastorino

railties/CHANGELOG.md

@@ -1,5 +1,7 @@
 ## Rails 3.2.0 (unreleased) ##
 
+*   Rails::Plugin is deprecated and will be removed in Rails 4.0. Instead of adding plugins to vendor/plugins use gems or bundler with path or git dependencies. *Santiago Pastorino*
+
 *   Guides are available as a single .mobi for the Kindle and free Kindle readers apps. *Michael Pearson & Xavier Noria*
 
 *   Allow scaffold/model/migration generators to accept a "index" and "uniq" modifiers, as in: "tracking_id:integer:uniq" in order to generate (unique) indexes. Some types also accept custom options, for instance, you can specify the precision and scale for decimals as "price:decimal{7,2}". *Dmitrii Samoilov*

railties/guides/source/3_2_release_notes.textile

@@ -67,6 +67,8 @@ When running a multi-user, multi-account application, it's a great help to be ab
 
 h3. Railties
 
+* Rails::Plugin is deprecated and will be removed in Rails 4.0. Instead of adding plugins to vendor/plugins use gems or bundler with path or git dependencies.
+
 * Speed up development by only reloading classes if dependencies files changed. This can be turned off by setting <tt>config.reload_classes_only_on_change</tt> to false.
 
 * New applications get a flag <tt>config.active_record.auto_explain_threshold_in_seconds</tt> in the environments configuration files. With a value of <tt>0.5</tt> in <tt>development.rb</tt> and commented out in <tt>production.rb</tt>. No mention in <tt>test.rb</tt>.

railties/lib/rails/plugin.rb

@@ -53,6 +53,7 @@ def railtie_name
     end
 
     def initialize(root)
+      ActiveSupport::Deprecation.warn "Plugins are deprecated and will be removed in Rails 4.0. Use gems instead or bundler with path or git dependencies."
       @name = File.basename(root).to_sym
       config.root = root
     end