Fixes bug with sprite name collision

If the sprite name is the same name as any of the files in the sprite, then the sprite creation will fail.

This fix checks for this and adds to the file name to prevent the collision for Sprites and Bundles.
Merge branch 'master' of https://github.com/jlestein/WebEssentials2013

Conflicts:
	EditorExtensions/Images/MenuItems/SpriteImage.cs