fix jar caching forcing default textures (caused by 183da128)
Fixed pngnq rename error in Windows

Fixed error 183 (File already exists) in Windows when trying to use
pngnq and trying to rename "file.png.tmp" to "file.png".
Merge pull request #1102 from Shadark/rename_fix

Fixed pngnq rename error in Windows
Use `is not None` instead of `!= None`
Try to prevent findGitHash from ever returning None
Try to prevent findGitHash from ever returning None

See #1093