fixed buildResponderList: in CCResponderManager

previously *buildResponderList:* overlooked adding the current node to the responder list if the node *only* contained children with a negative z-index while having interactions enabled.
 
flagging the node for possible addition, then eventually adding it should patch this.
 
and some minimisations.
Merge branch 'patch-1' of https://github.com/kalo/cocos2d-iphone into v3.0