Enhance CJSON with JsonSerializable support (#2540)
Encoding a JsonSerializable object will now have it's serializable result
encoded by CJSON.
Added a guard to prevent the autoload bug as mentioned by @cebe.
Added unit test.
Merge branch '2540-CJSON-JsonSerializable' of https://github.com/SamMousa/yii into SamMousa-2540-CJSON-JsonSerializable
Merge branch '2540-CJSON-JsonSerializable' of https://github.com/SamMousa/yii into SamMousa-2540-CJSON-JsonSerializable