libavfilter/libmpcodecs: remove unused files

Signed-off-by: Paul B Mahol <onemda@gmail.com>
avcodec/mjpegdec: change error return value to be outside the 16bit range

Fixes part of Ticket2965

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/mjpegdec: rgba64 ljpeg support

Fixes Ticket2965

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