fix bugs about CCMenu

1. CCMenu::setHandlerPriority(int) has the same effect whit CCMenu::setTouchPriority(int), but the code in CCMenu::setHandlerPriority(int) will cause assert error when it is called before CCMenu::registerWithTouchDispatcher()
2. menuItems in CCMenu will still activate or re-selected when CCMenu is set to disable after CCMenu::ccTouchBegan()