Rework single sign out support to work in Rails 3.1.
Switch session ID store from a filter to rack middleware. Automatically inject into the stack via a railtie.
Decouple ActiveRecord dependency of #destroy_session_by_id.

When ActiveRecord isn't included in the project, a NameError is thrown
(uninitialized constant ActiveRecord)
Fix for RedisStore 1.1.0. Typo when error occurrs.
Loop through @backend and @app middlewares until find session instance.
Support CacheStore on single sign out.
Merge branch 'master' of https://github.com/endel/devise_cas_authenticatable into endel-master

Conflicts:
	app/controllers/devise/cas_sessions_controller.rb