Fix handling of input if not in native endianness, and add support for
9/10-bit output. This allows us to force endianness of YUV420P 9/10bit
in the H264/10bit fate tests, which should fix them on big-endian
systems.
This moves some groups of tests for single codecs to separate files,
and adds shorthands for running all tests in a group.
Originally committed as revision 24697 to svn://svn.ffmpeg.org/ffmpeg/trunk
