That way gitUpdater could be used to extract most recent published
releases for .nix files that don't use git directly to define builds.
An example is iproute2 package which does not have a single place
to lookup most recent release.
- 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'