Sync some fixes from master branch

master PR URL: https://github.com/cocos2d/cocos2d-x/pull/2784
* Adding libwebsockets license in WebSocket.h/.cpp.
* Log error instead of triggering an assert for shadow and stroke.
* [Mamarlade] Fixing a compilation error in cocos2dx/platform/marmalade
* Fixing a bug that display is wrong when setting setTexture(NULL) for CCSprite
* [Spine] Using getContentSize to make spine-runtime supports the strategy of loading resources in cocos2d-x.
* Removing CODE_SIGN_IDETITY section in prom.pbxproj.
* Marmalade projects fix.