Fixed #4857: Add check to cc._setup to avoid double invocation
Merge branch 'develop-3.0' of git://github.com/cocos2d/cocos2d-html5 into develop-3.0
Fixed #4670: Null callback check added in Canvas addImage function
Merge pull request #1779 from pandamicro/develop-3.0

Fixed #4857: Add check to cc._setup to avoid double invocation