jpegls: support YCbCr 2:1:1 color transform

[ami_stuff]

I was able to create jls YCbCr 2:1:1 sample (see ticket #893)

C:\>ffmpeg -i YCbCr_211_lossy.jls
ffmpeg version N-54658-g43d3659 Copyright (c) 2000-2013 the FFmpeg developers
  built on Jul 12 2013 02:23:12 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. 39.100 / 52. 39.100
  libavcodec     55. 18.102 / 55. 18.102
  libavformat    55. 12.101 / 55. 12.101
  libavdevice    55.  3.100 / 55.  3.100
  libavfilter     3. 80.100 /  3. 80.100
  libswscale      2.  3.100 /  2.  3.100
  libswresample   0. 17.102 /  0. 17.102
  libpostproc    52.  3.100 / 52.  3.100
[jpegls @ 0x20e6480] Subsampling in JPEG-LS is not implemented. Update your FFmp
eg version to the newest one from Git. If the problem still occurs, it means tha
t your file has a feature which has not been implemented.
[image2 @ 0x200a900] decoding for stream 0 failed
[image2 @ 0x200a900] Could not find codec parameters for stream 0 (Video: jpegls
): unspecified size
Consider increasing the value for the 'analyzeduration' and 'probesize' options
YCbCr_211_lossy.jls: could not find codec parameters