jpeg: support some more pix fmts

[ami_stuff]

created with

cjpeg -sample 3x1/[...] test.tga >test_31.jpg

C:\>ffmpeg -i test_31.jpg
ffmpeg version N-47325-gb90e795 Copyright (c) 2000-2012 the FFmpeg developers
  built on Dec  1 2012 02:23:25 with gcc 4.5.0 (GCC) 20100414 (Fedora MinGW 4.5.
0-1.fc14)
  configuration: --prefix=/var/www/users/research/ffmpeg/snapshots/build --arch=
x86 --target-os=mingw32 --cross-prefix=i686-pc-mingw32- --cc='ccache i686-pc-min
gw32-gcc' --enable-w32threads --enable-memalign-hack --enable-runtime-cpudetect
--enable-cross-compile --enable-static --disable-shared --extra-libs='-lws2_32 -
lwinmm -lpthread' --extra-cflags='--static -I/var/www/users/research/ffmpeg/snap
shots/build/include' --extra-ldflags='-static -L/var/www/users/research/ffmpeg/s
napshots/build/lib' --enable-bzlib --enable-zlib --enable-gpl --enable-version3
--enable-nonfree --enable-libx264 --enable-libspeex --enable-libtheora --enable-
libvorbis --enable-libfaac --enable-libxvid --enable-libopencore-amrnb --enable-
libopencore-amrwb --enable-libmp3lame --enable-libvpx --disable-decoder=libvpx
  libavutil      52. 10.100 / 52. 10.100
  libavcodec     54. 78.100 / 54. 78.100
  libavformat    54. 41.100 / 54. 41.100
  libavdevice    54.  3.101 / 54.  3.101
  libavfilter     3. 23.104 /  3. 23.104
  libswscale      2.  1.103 /  2.  1.103
  libswresample   0. 17.101 /  0. 17.101
  libpostproc    52.  2.100 / 52.  2.100
[mjpeg @ 0x1eec980] Unhandled pixel format 0x31111100
[image2 @ 0x1eebe20] decoding for stream 0 failed
[image2 @ 0x1eebe20] Could not find codec parameters for stream 0 (Video: mjpeg,
 1024x768 [SAR 1:1 DAR 4:3]): unspecified pixel format
Consider increasing the value for the 'analyzeduration' and 'probesize' options
test_31.jpg: could not find codec parameters

[ami_stuff]

test_41.jpg works with this (4:1:1 41:11:11):

    case 0x41111100:
//    case 0x14111100:
        s->avctx->pix_fmt = AV_PIX_FMT_YUV411P;
        s->avctx->color_range = s->cs_itu601 ? AVCOL_RANGE_MPEG : AVCOL_RANGE_JPEG;
        break;

test_14.jpg (4:1:1 14:11:11) needs some tweaks.