fate: make lavfi tests output only md5
Instead of saving huge raw files, use the md5: output pseudo-protocolto calculate the checksum of the file directly. This is especiallyuseful when testing on remote targets as it avoids transferring 3.6GBover the network.
Add some ad-hoc tests for libavfilter.
A patched version of ffmpeg supporting video filters is required forgetting this working; thus make lavfitest is supposed to work only inthe libavfilter repository for now.
Originally committed as revision 22586 to svn://svn.ffmpeg.org/ffmpeg/trunk