Not sure what I did in 3e4e1bde69 but that
updated XFAIL is now an XPASS on NVidia. Because, apparently, the clear
clears the whole memory, not just the image area, so even though the row
pitch is different, the comparison of the initial N bytes passes.
So I'm ditching the silly XFAILs and doing a proper image comparison that
includes the actual driver-dependent row pitch for the images. Finally,
the image-to-image copy was flat out wrong because it didn't take the
*input* row pitch into account, so it copied garbage and then compared to
a different kind of garbage.
Vladimír Vondruš
64ed7d183b