Use class constants for Event declatration in ActionFiler

framework/yii/base/ActionFilter.php

@@ -30,8 +30,8 @@ class ActionFilter extends Behavior
 	public function events()
 	{
 		return array(
-			'beforeAction' => 'beforeFilter',
+			Controller::EVENT_BEFORE_ACTION => 'beforeFilter',
-			'afterAction' => 'afterFilter',
+			Controller::EVENT_AFTER_ACTION => 'afterFilter',
 		);
 	}