Explicitly test for ActionController::Base in addition to Rails

The code uses ActionController::Base, but it is possible to have Rails
defined, but not ActionController::Base. In the old situation, the code
would have raised due to ActionController::Base not being defined.

lib/casclient.rb

@@ -68,7 +68,7 @@ def method_missing(name, *args)
 require 'casclient/client'
 require 'casclient/tickets/storage'
 autoload :ACTIVE_RECORD_TICKET_STORE, 'casclient/tickets/storage/active_record_ticket_store'
-if defined?(Rails)
+if defined?(Rails) && defined?(ActionController::Base)
   require 'casclient/frameworks/rails/filter'
   require 'casclient/frameworks/rails/cas_proxy_callback_controller'
 end