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

Conflicts:
	extensions/CocoStudio/GUI/UIWidgets/UIButton.js
	extensions/CocoStudio/GUI/UIWidgets/UIImageView.js
	extensions/CocoStudio/GUI/UIWidgets/UILoadingBar.js
	extensions/CocoStudio/GUI/UIWidgets/UISlider.js
	extensions/GUI/CCControlExtension/CCControlSwitch.js
Fixed #3371: remove "ie" from cc.Browser.webglWhiteList
Merge branch 'develop' of https://github.com/cocos2d/cocos2d-html5 into Iss3371_xxxConst
Merge branch 'develop' of https://github.com/cocos2d/cocos2d-html5 into Iss3371_xxxConst
Issue #3371: replace types of cc.Node's anchorPoint, anchorPointInPoint and Position from cc.Point to cc._PointConst
Issue #3371: replace cc.Node's contentSize from cc.Size to cc._SizeConst
Merge branch 'develop' of https://github.com/cocos2d/cocos2d-html5 into Iss3371_xxxConst
Closed #3371: modify jsloader.js path
Merge pull request #1329 from dingpinglv/Iss3371_xxxConst

Closed #3371: adding cc._PointConst and cc._SizeConst to engine for better Performance.