y41p encoder and decoder

y41p is a packed 12-bit 4:1:1 YUV format used by Brooktree.

Fixes issue 1123 / ticket #102.

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

libavformat/riff.c

@@ -290,6 +290,7 @@ const AVCodecTag ff_codec_bmp_tags[] = {
     { CODEC_ID_VBLE,         MKTAG('V', 'B', 'L', 'E') },
     { CODEC_ID_ESCAPE130,    MKTAG('E', '1', '3', '0') },
     { CODEC_ID_DXTORY,       MKTAG('x', 't', 'o', 'r') },
+    { CODEC_ID_Y41P,         MKTAG('Y', '4', '1', 'P') },
     { CODEC_ID_NONE,         0 }
 };