Closed #3546: Added bake function to cc.Layer
Merge branch 'develop' of https://github.com/cocos2d/cocos2d-html5 into Iss3646_BakeNode
Closed #3646: modify cc.Layer to avoid the normal layer when it doesn't use bake function.
Merge pull request #1931 from dingpinglv/Iss3646_BakeNode

Closed #3546: Added bake function to cc.Layer