Fix skipping of default values for extra props

Values from "extra props", i.e. those where dontSetInEditor is
set to YES, were always written to the file, even if the value
was equal to the default serialization.
Merge branch 'fix_skipping_extra_props' of https://github.com/theGoodEvil/CocosBuilder into develop
Removed debug traces
Fixes bug when regenerating sprite sheets.
Removes debug traces
Merge pull request #9 from cocos2d/develop

merge 24/4