[1/2] gdiplus: Add some tests for scaling an image with various pixel offset modes. Take 3.

[Vincent Povirk]

> Can I please get a feedback on this gdiplus series along with another one
> "gdiplus: Add some tests for GIF properties." ?

Yeah, I don't know why those patches would still be New. I didn't look
carefully, but it all seemed fine to me.

As far as what you're doing with pixel offsets, I haven't verified
that's how it works but it seems likely (and probably equally applies
to the other interpolation modes). The discrepancy is probably because
we're not applying pixel offsets to destination co-ordinates, which
we'll have to do eventually.