ext/ffmpeg/gstffmpegprotocol.c: Some "seeking" hacks, and separate peek from read (read = peek + flush) so seek can u...

Original commit message from CVS:
* ext/ffmpeg/gstffmpegprotocol.c: (gst_ffmpegdata_peek),
(gst_ffmpegdata_read), (gst_ffmpegdata_seek):
Some "seeking" hacks, and separate peek from read (read = peek +
flush) so seek can use peek as well to workaround typefind. With
this, I'm able to play several of the gaming format movies in
Totem.