Test program for stressing the use of different formats and operators

Test program for stressing the use of different formats and operators

The code and overall method is mostly based on scaling-test. This one
focuses on trying to stress as many different color formats and types
of composition operations as possible.

This is an initial implementation which may need more tuning. Also
not all color format and operator combinations are actually used.

When cpu specific optimizations are disabled, this test provides
identical deterministic results on x86, PPC and ARM.

Script blitters-test-bisect.rb now works in non-stop mode, until
it finds any problem. This allows to run it for example overnight
in order to test a lot more variants of pixman calls and increase
chances of detecting problems in pixman. Just like with scaling-test,
running blitters-test binary alone with no command line arguments
runs a small predefined number of tests and compares checksum
with a reference value for quick verification.