handle breaking force.
incompatible file version throws an exception

prevents the generic assert in addChild because child is nil which doesn't exactly say why this is happening
Joints support collideBodies.
Merge branch 'develop-v3' of https://github.com/apportable/cocos2d-iphone into develop-v3
update cocos2d
Merge branch 'develop-v3' of https://github.com/apportable/cocos2d-iphone into develop-v3