Fix regression in EditableTileMapAtlas where UpdateAtlasValues is called multiple times from setting the Directory causing a Key Already Exists error.
Fix regression in EditableTileMapAtlas where UpdateAtlasValues is called multiple times from setting the Directory causing a Key Already Exists error.

+ Added new method that takes an x,y offset instead of having to create CCGridSize objects all over the place just to reference the tiles.

MSylvia/CocosSharp,MSylvia/CocosSharp,zmaruo/CocosSharp,hig-ag/CocosSharp,haithemaraissia/CocosSharp,TukekeSoft/CocosSharp,TukekeSoft/CocosSharp,netonjm/CocosSharp,mono/CocosSharp,hig-ag/CocosSharp,haithemaraissia/CocosSharp,zmaruo/CocosSharp,mono/CocosSharp,netonjm/CocosSharp