Fix for SpriteKit texture atlases.  We were not finding the supporting image because in the example the image name was Backgrounds.1.png.  Once we strip off the .png the AddImage will then strip off the .1 as well assuming it is the file extension instead of part of the file name.  The .1 in the file name causes the loading problem.
Fix for SpriteKit texture atlases.  We were not finding the supporting image because in the example the image name was Backgrounds.1.png.  Once we strip off the .png the AddImage will then strip off the .1 as well assuming it is the file extension instead of part of the file name.  The .1 in the file name causes the loading problem.

Fix https://github.com/mono/CocosSharp/issues/326

mono/CocosSharp,mono/CocosSharp