Revert "vf_interlace: deprecate lowpass option"

This reverts commit 35b05c5184fb3aa1191e2d1e7f1cae1e11f344a4.
A warning is introduced in case this option is used.
pngdec: correctly indent macros
pixdesc: K&R formatting cosmetics

Also change some comments to multiline.

Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>
h264: prevent theoretical infinite loop in SEI parsing

Properly address CVE-2011-3946 and parse bitstream as described in the spec.

CC: libav-stable@libav.org
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind