lavfi: add lut3d filter.

Fixes part of Ticket #2517.
v4l2: make possible to disable libv4l2 at runtime.

Also disable it by default since it looks currently buggy. The
usefulness of such library is mostly limited to backward compatibility
with very old devices.
smvjpegdec: use av_pix_fmt_desc_get() avoid direct table access

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
proresdec: Fix end condition

Fixes out of array writes
No FFmpeg release is affected by this

This also fixes some artifacts

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>