Issue #2416: refactor cc.RenderTexture
Merge branch 'Iss2416_RefactorRenderer' of https://github.com/dingpinglv/cocos2d-html5 into Iss2416_RefactorRenderer
Issue #2416: correct some mistakes of cc.RenderTexture and cc.Layer
Merge branch 'Iss2416_RefactorRenderer' of https://github.com/dingpinglv/cocos2d-html5 into Iss2416_RefactorRenderer