[nacltoons] Use box2d sensors to detect collisions.

Also, roll cocos2dx version, now that our port has been upstreamed.

BUG=None

Review URL: https://codereview.chromium.org/12387095

git-svn-id: https://nativeclient-sdk.googlecode.com/svn/trunk/src@1516 050acbb0-2703-11df-ab0a-9f3f633ae91d