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 copy filter, useful for testing the avfilter_draw_slice() copycode.
Originally committed as revision 26112 to svn://svn.ffmpeg.org/ffmpeg/trunk