bug#57400: 29.0.50; Support sending patches from VC directly

[Eli Zaretskii]

> Cc: 57400@debbugs.gnu.org, Antoine Kalmbach <ane@iki.fi>
> From: Lars Ingebrigtsen <larsi@gnus.org>
> Date: Tue, 04 Oct 2022 01:32:15 +0200
> 
> Philip Kaludercic <philipk@posteo.net> writes:
> 
> > I had forgotten about `previous-revision', so that was easy and I
> > decided to fall back to a generic subject as that can be easily revised:
> 
> I haven't tested it, but it looks good to me, so feel free to push when
> you feel it's ready (after adding documentation and a NEWS item).

Please allow some time for patch review and comments, there's no
reason to rush ahead with such a significant new feature.  Ideally,
Dmitry should chime in.