CCTextField set textfield visibility and enabled

show/hide the UITextField if it's responsible node or a related ancestor is visible/invisible

i'm not too happy about this implementation but not much that can be done, right now, about the polling method to control visibility.

also set the textfield's usability along with the enabled property of the control.

issue from the forums, http://forum.cocos2d-iphone.org/t/cctextfield-remains-visible-when-parent-is-not-visible/13139