turning into a funtioning Rails plugin

init.rb

@@ -0,0 +1 @@
+require 'cancan'

lib/cancan.rb

@@ -1,8 +1,7 @@
-$:.unshift(File.dirname(__FILE__))
-require 'cancan/instance_exec'
-require 'cancan/ability'
-require 'cancan/controller_additions'
-
 module CanCan
   class AccessDenied < StandardError; end
-end
+end
+
+require File.dirname(__FILE__) + '/cancan/instance_exec'
+require File.dirname(__FILE__) + '/cancan/ability'
+require File.dirname(__FILE__) + '/cancan/controller_additions'

lib/cancan/controller_additions.rb

@@ -35,6 +35,8 @@ module CanCan
   end
 end
 
-class ActionController::Base
-  include CanCan::ControllerAdditions
-end
+if defined? ActionController
+  ActionController::Base.class_eval do
+    include CanCan::ControllerAdditions
+  end
+end