* added --intf option to vlc

 * added --intf option to vlc
 * started cleaning vout_sdl.c
 * the dummy plugin works again
 * added a slider to the Gnome interface so that we can browse through streams

  There is a problem with the slider: we sometimes get unexpected async
  replies, which would mean that we don't properly lock our Xlib calls.
  Which is true. But we also get these errors when using `--vout dummy'.
  I'll investigate.