add rgb suffix handling for demuxer

Originally committed as revision 9103 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/raw.c

@@ -881,7 +881,7 @@ AVInputFormat rawvideo_demuxer = {
     rawvideo_read_packet,
     raw_read_close,
     .flags= AVFMT_GENERIC_INDEX,
-    .extensions = "yuv,cif,qcif",
+    .extensions = "yuv,cif,qcif,rgb",
     .value = CODEC_ID_RAWVIDEO,
 };