Add the open_id_authentication plugin

The plugin is taken from http://github.com/rails/open_id_authentication
commit 079b91f70602814c98d4345e198f743bb56b76b5 

This plugin provides some convenience wrapper functions around
the ruby gem ruby-openid

vendor/plugins/open_id_authentication/init.rb

@@ -0,0 +1,18 @@
+if config.respond_to?(:gems)
+  config.gem 'ruby-openid', :lib => 'openid', :version => '>=2.0.4'
+else
+  begin
+    require 'openid'
+  rescue LoadError
+    begin
+      gem 'ruby-openid', '>=2.0.4'
+    rescue Gem::LoadError
+      puts "Install the ruby-openid gem to enable OpenID support"
+    end
+  end
+end
+
+config.to_prepare do
+  OpenID::Util.logger = Rails.logger
+  ActionController::Base.send :include, OpenIdAuthentication
+end