Use to_sentence rather than inspect when reporting which registered plugins are missing

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@6291 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

railties/lib/plugin/locator.rb

@@ -46,7 +46,7 @@ def ensure_all_registered_plugins_are_loaded!(loaders)
             unless registered_plugins.nil? || registered_plugins.empty?
               missing_plugins = registered_plugins - loaders.map(&:name)
               unless missing_plugins.empty?
-                raise LoadError, "Could not locate the following plugins: #{missing_plugins.inspect}"
+                raise LoadError, "Could not locate the following plugins: #{missing_plugins.to_sentence}"
               end
             end
           end