lavc: deprecate CODEC_CAP_NEG_LINESIZES

It was never used in any codec since it was added 3 years ago.
lavc: update coded_frame doxy.

It is not used during decoding anymore.
Replace all instances of avcodec_alloc_frame() with av_frame_alloc().
lavc: deprecate avcodec_alloc_frame().
a64multienc: use the AVFrame API properly.
asvenc: use the AVFrame API properly.
avs: use the AVFrame API properly.
bethsoftvid: use the AVFrame API properly.
c93: use the AVFrame API properly.
cdxl: remove an unused variable
cinepak: use the AVFrame API properly.
cljr: use the AVFrame API properly.
qtrle: use the AVFrame API properly.
escape124: use the AVFrame API properly.
msvideo1: use the AVFrame API properly.
cin video: use the AVFrame API properly.
qpeg: use the AVFrame API properly.
dxa: use the AVFrame API properly.
jvdec: use the AVFrame API properly.
FATE: add a jv test