various subband encoders (all either worse or complicated so they are commented out)

different 0-context encoding, 1.2% lower bitrate (foreman@352x288 qscale=8) no significant change at qscale=1


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@3366 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b