flac fourcc (fixes mplayer -demuxer 35 with flac)

Originally committed as revision 6569 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/riff.c

@@ -191,6 +191,7 @@ const CodecTag codec_wav_tags[] = {
     { CODEC_ID_ADPCM_CT, 0x200 },
     { CODEC_ID_ADPCM_SWF, ('S'<<8)+'F' },
     { CODEC_ID_TRUESPEECH, 0x22 },
+    { CODEC_ID_FLAC, MKTAG('f', 'L', 'a', 'C') },
 
     // for NuppelVideo (nuv.c)
     { CODEC_ID_PCM_S16LE, MKTAG('R', 'A', 'W', 'A') },