libx264: Implement rgb24 support through a seperate AVCodec.

This avoids people mistakely encoding in a way that many players dont support.
Fixes Ticket658

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/allcodecs.c

@@ -402,6 +402,7 @@ void avcodec_register_all(void)
     REGISTER_ENCODER (LIBVORBIS, libvorbis);
     REGISTER_ENCDEC  (LIBVPX, libvpx);
     REGISTER_ENCODER (LIBX264, libx264);
+    REGISTER_ENCODER (LIBX264RGB, libx264rgb);
     REGISTER_ENCODER (LIBXAVS, libxavs);
     REGISTER_ENCODER (LIBXVID, libxvid);