More optimizations in the collision code and fix for sensor test.
Merge branch 'master' of https://github.com/Cocos2DXNA/cocos2d-xna
Merge pull request #302 from Cocos2DXNA/SENSOR_TEST_FIX

Sensor test fix
Merge branch 'master' of https://github.com/Cocos2DXNA/cocos2d-xna