This makes only tests actually using avconv depend on it.
The remaining tests already depend on what they need.
Signed-off-by: Mans Rullgard <mans@mansr.com>
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
