- Add the 'gitUpdater' helper function to update git based packages, using the
'genericUpdater' function.
- Rework argument passing to the `list-git-tags' and 'list-archive-two-level-versions' scripts.
- Replace 'genericUpdater' plus 'list-git-tags' by 'gitUpdater'
After making `ffmpeg` point to the latest `ffmpeg_4`, all packages that
used `ffmpeg` without requiring a specific version now use ffmpeg_3
explicitly so they shouldn't change.