Each fate-seek test depends now only on the corresponding fate-acodec,
fate-vsynth2 or fate-lavf test which creates the file seek-tests
operates on. The tests and references are renamed to match the test they
depend on.
Seeking on image sequences doesn't actually work, so this
test isn't very useful until that capability is added.
Originally committed as revision 22286 to svn://svn.ffmpeg.org/ffmpeg/trunk