[Fluxus] texture problems

[gabor papp]

> If you texture a model in blender and then export it into fluxus,
> with the flip the texture coords and texture pixels match, whereas
> previously they didn't
then it seems i have to get used to this and start converting my scripts
that use pixels :). it would be nice to put a warning about this in the
documentation and the inline help.

i cherry-picked scott's png save modification to the main branch.

best,
gabor