adding 'cannot?' method which performs opposite check of 'can?' - closes #1

lib/cancan/ability.rb

@@ -21,6 +21,10 @@ module CanCan
       false
     end
     
+    def cannot?(*args)
+      !can?(*args)
+    end
+    
     def possible_actions_for(initial_action)
       actions = [initial_action]
       (@aliased_actions || default_alias_actions).each do |target, aliases|

lib/cancan/controller_additions.rb

@@ -1,7 +1,7 @@
 module CanCan
   module ControllerAdditions
     def self.included(base)
-      base.helper_method :can?
+      base.helper_method :can?, :cannot?
     end
     
     def unauthorized!
@@ -16,6 +16,10 @@ module CanCan
       (@current_ability ||= current_ability).can?(*args)
     end
     
+    def cannot?(*args)
+      (@current_ability ||= current_ability).cannot?(*args)
+    end
+    
     def load_resource # TODO this could use some refactoring
       unless params[:action] == "index"
         if params[:id]