Initial implementation of authorization adapter
Added authorization to Pages
Started on the CanCan adapater
Added tests and docs
Fix error message
authorization_adapter documentation additions
Added #normalized to help in simple matching in auth adapters.

The `#authorized?` method's subject can be set to both instances as well
as classes of objects. This can make it much difficult to create simple
case statements for authorization since you have to handle both the
class level match and the instance level match.

For example:

    class MyAuthAdapter < ActiveAdmin::AuthorizationAdapter

      def authorized?(action, subject = nil)
        case subject
        when Post
          true
        when Class
          if subject == Post
            true
          end
        end
      end

    end

To handle this, the normalized method takes care of returning a lambda
which implements `===` to be matched in a case statement.

The above now becomes:

    class MyAuthAdapter < ActiveAdmin::AuthorizationAdapter

      def authorized?(action, subject = nil)
        case subject
        when normalized(Post)
          true
        end
      end

    end
Added additional docs
Merge branch 'authorization-documentation' into authorization-adapter
Added authorization docs for Actions and Authorization methods
Added support for #normalized matcher in ruby 1.8

Ruby 1.8 Proc's do not implement === like they do in Ruby 1.9. Instead
of using a Proc, we now implement our own matching class with ===.
Merge branch 'master' into authorization-adapter
Merge branch 'master' into authorization-adapter

Conflicts:
	lib/active_admin/page_controller.rb
	lib/active_admin/resource_controller/collection.rb
	spec/unit/resource_controller/data_access_spec.rb
Implemented configurable access denied handling.

* Added config.on_unauthorized_access to the inheritable configurations
  for Active Admin.
* Added a test suite for MethodOrProcHelper
* Implemented default access denied handling for HTML, JSON, and XML
Documentation updates for Authorization Adapters
Removed unused code block in DSL related to Authorization adapters
Merge pull request #1817 from gregbell/authorization-adapter

Conflicts:
	lib/active_admin/resource_controller/decorators.rb