Export all images right-side up. OpenGL flips them because fail, so we
have to do a bit of work to correct that. Thankfully, this operation is
not as slow as I thought.
NOTE TO SELF: remember, texture page updating would be nice to have...
Yeah, korlib was a bit faster than this implementation, but, honestly,
having a second python module made life more difficult than it needed to
be. This fixes that.