#16 Port to avconv

[quadrispro]

videotrans depends on ffmpeg which no longer built by libav in Debian. This will
render videotrans unusable soon in unstable.

Can you please review the patch available here?
http://anonscm.debian.org/gitweb/?p=pkg-multimedia/videotrans.git;a=commitdiff;h=71cb6e339379765904e7d7f3097d0e41bdfe91a8

Thanks for considering.