bug#34944: 27.0.50; FR: support amend in vc-hg

[Eli Zaretskii]

> From: Richard Stallman <rms@gnu.org>
> Cc: p.stephani2@gmail.com, 34944@debbugs.gnu.org
> Date: Fri, 22 Mar 2019 22:34:04 -0400
> 
>   > > The Git integration for vc.el supports amending commits via a magic
>   > > changelog header.
> 
> What does this mean, concretely?

That a specially formatted header in the VC log buffer signals VC to
make the next checkin operation replace the last commit instead of
adding a new commit.  See vc-git-log-edit-toggle-amend and
vc-git-checkin for the details.  It boils down to whether or not the
nezt "git commit" is invoked with the --amend switch.