avformat: use avcodec codec_tag as original fourcc

Fixes Bink video playback. The Bink video decoder in libavcodec relies
on the fourcc to determine the version of the codec.

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
Contribs: compile Bink decoder
Update NEWS for Bink and jpeg encoder
Add .bik extension registration