locks: ensure lock directory exists

Fixes #17326.
FormulaInstaller: wrap --build-from-source in an Option object

c.f. #17327.
mjpegtools: use new optional deps
youtube-dl add ffmpeg caveat

Remind that ffmpeg is needed if you want to use the post-processing options.

Closes #17283.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
git-flow AVH 1.4.2

Closes #16876.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
adol-c: remove old comment
adol-c: use Python one-liner instead of aardvark_shell_utils
style nit picks
abiword --devel 2.9.4
style nits
Merge remote-tracking branch 'upstream/master'