Closed #5832: Fixed a bug of RenderTexture that it doesn't support depthStencilFormat in v2.x
Merge branch 'v2.x' of https://github.com/cocos2d/cocos2d-html5 into Iss5800_StencilBug
Merge pull request #2140 from dingpinglv/Iss5832_RenderTextureV2

Closed #5832: Fixed a bug of RenderTexture that it doesn't support depthStencilFormat in v2.x