Merge pull request #878 from dingpinglv/Iss1615_WebGLRendering

fixed #1615 fixed a bug of cc.glBindTexture2DN and add setAdditionalTran...
fixed #1615 remove some error checks for WebGL, fixed issue #879 and fixed a bug of cc.LabelTTF when init method without parameters.
Merge branch 'master' of https://github.com/cocos2d/cocos2d-html5 into iss1615_WebGLRendering