Deprecate and mark for deletion the function guess_stream_format(),
and clone its code to ffserver_guess_format() in ffserver.c.
guess_stream_format() is hackish since it relies on some undocumented
properties of the name of the muxers (wich is currently only relevant
for the ASF muxer), and has no use outside ffserver.c.
Originally committed as revision 20987 to svn://svn.ffmpeg.org/ffmpeg/trunk