Add filename to test output when results change

In commit d3551b8 I added the script name to the output when a test
failed to evaluate a script, but I didn't account for successfully
processed scripts that simply differ from the previous result.
Fix frame hashing to account for planar frames
Generate YUV test clips directly in YUV space

Eliminates starting in RGB and converting, which in turn eliminates
"image too small" errors when converting very small clips, which an
upcoming commit would otherwise encounter.
Fix mode parameter for planar formats beyond YV12

The broken code I'd been using just so happened, by virtue of the
numbers involved, to work for YV12. That was the only planar YUV format
in AVS 2.5, but when I added 2.6 support I obviously didn't check my
results well. More justification for these regression tests!
Correct and simplify tileCtr calculations

Another oversight that only coincidentally hid itself through careless
testing of planar formats beside YV12. Processing YV411, with its four
pixel wide luma block, revealed the rounding problem.
Clean up Y8/YV24 mode behavior

Y8 now allows mode one, to bring its presentation in line with YV24, and
both get forced to that mode if the user specifies zero. With only one
luma sample, modes zero and one are identical for those formats, might
as well avoid the unnecessary division.
Add regression tests for mode parameter

I'm abandoning my previous idea to separate the scripts and reference
data from the code changes; doesn't help the way I'd hoped it would, and
I think in principle all the changes related to one set of tests should
be lumped together.