Easier to define non-Model related abilities, such

as :administer_site for example, which is only
based on the user object.

I wanted to be able to set specific abilities that
are not related to any specific model, but rather
based on the user object alone. Why use cancan for
that though? Cause I like having all my ability
definition in one place, cause then there's just
one if statement to modify instead of multiple
if statements all over acting directly on the user
object.

It was doable with cancan, but you had to call
`can?(:administer, nil)` as the second argument
was not optional. So I simply removed the need
for the second argument by defaulting it to nil.

lib/cancan/ability.rb

@@ -40,7 +40,7 @@ module Ability
     #     assert ability.cannot?(:destroy, Project.new)
     #   end
     # 
-    def can?(action, noun)
+    def can?(action, noun = nil)
       (@can_definitions || []).reverse.each do |base_behavior, defined_action, defined_noun, defined_block|
         defined_actions = expand_actions(defined_action)
         defined_nouns = [defined_noun].flatten
@@ -103,7 +103,7 @@ def cannot?(*args)
     #   can :read, :stats
     #   can? :read, :stats # => true
     # 
-    def can(action, noun, &block)
+    def can(action, noun = :all, &block)
       @can_definitions ||= []
       @can_definitions << [true, action, noun, block]
     end
@@ -120,7 +120,7 @@ def can(action, noun, &block)
     #     product.invisible?
     #   end
     # 
-    def cannot(action, noun, &block)
+    def cannot(action, noun = :all, &block)
       @can_definitions ||= []
       @can_definitions << [false, action, noun, block]
     end