Originally it was just assuming that any Vector3ub or Color3ub is a
normalized format. That was kinda enough for many cases, but it started
to get annoying with sRGB image comparisons, as those had to be
manually reinterpret with a sRGB-less format in order to pass.
Now the pixel format detection looks at the expected image format as
well, and if the underlying type and component count matches, it
inherits the sRGB and normalized property from it as well. If not, it
falls back to an integer format for vectors, and normalized format for
colors. For vectors this is different from previous behavior but
shouldn't cause any problem in practice -- the only result will be that
the image comparison fails with a different message for pixel format
mismatch than before.
This now also properly and fully tests the pixelFormatFor() helper, and
adds a missing Color3 specialization of it.
Vladimír Vondruš
f589aa1a5d