Some tests were failing because the color was not read correctly from
a QImage. To make it possibly to read more accurate colors a pixel
accessor returing QColor has been added.
Some tests also had the wrong order of arguments, confusing dest and src
formats. This has been corrected, so they test what they claim to test.
A test for RGB30 linear gradients is also added.
Change-Id: Ic623ae1b8e0bf7383056b641c6e8230a1d7dd0dd
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>