avfilter/vf_aspect: remove dupe constants setup

Signed-off-by: Paul B Mahol <onemda@gmail.com>
lavc: remove dead FF_API_ALLOC_CONTEXT API
lavc: remove dead FF_API_AVCODEC_OPEN API
lavc: remove dead FF_API_OLD_TIMECODE API
ffmpeg: add verbose consistency checks in case of filtering inconsistent options

In particular, warn in case -filter and streamcopy is used at the same
time, fix trac ticket #678.