Add rails.js driver to default source list

actionpack/lib/action_view/helpers/asset_tag_helper.rb

@@ -140,7 +140,7 @@ module AssetTagHelper
         :stylesheets_dir => "#{assets_dir}/stylesheets",
       }
 
-      JAVASCRIPT_DEFAULT_SOURCES = ['prototype', 'effects', 'dragdrop', 'controls'].freeze unless const_defined?(:JAVASCRIPT_DEFAULT_SOURCES)
+      JAVASCRIPT_DEFAULT_SOURCES = ['prototype', 'effects', 'dragdrop', 'controls', 'rails'].freeze unless const_defined?(:JAVASCRIPT_DEFAULT_SOURCES)
 
       # Returns a link tag that browsers and news readers can use to auto-detect
       # an RSS or ATOM feed. The +type+ can either be <tt>:rss</tt> (default) or