Merge pull request #1329 from dingpinglv/Iss3371_xxxConst

Closed #3371: adding cc._PointConst and cc._SizeConst to engine for better Performance.
Fixed #3371: Correct some mistakes for _PointConst
Merge branch 'develop' of https://github.com/cocos2d/cocos2d-html5 into Iss3371_xxxConst