Commit Briefs
rework the vc-dir handling and remove the ugly hack
With this our *vc-dir* looks more like the others. Instead of showing something like stage:edit we only add `M', `D' or `A' (the got status flags), and so we don't need the ugly hack too.
add the required "headers" for a package
Emacs 27.1 is a prerequisite because of flatten-list, otherwise it should run on 25.1 onwards.
implement unregister
Even if it isn't really useful (it's only used in vc-transfer-file AFAICS) but it's easy to do and maybe can help someone eventually. See also github pr #7 for more background.