bug#39380: 26.3: Opening files in vc-dir-mode with differing root and working dir fails

[Eli Zaretskii <eliz@gnu.org>]

> Cc: 39380@debbugs.gnu.org, Wolfgang.Scherer@gmx.de
> From: Dmitry Gutov <dgutov@yandex.ru>
> Date: Sat, 8 Feb 2020 12:36:46 +0300
> 
> > If I say "hg status" in a subdirectory, I by default get file names
> > relative to the root.  Wouldn't Mercurial users be surprised that
> > Emacs produces a different display?  (I understand that there's a
> > recent tendency to make it easier to produce relative file names, and
> > there's even a config option to make that the default, but I'm asking
> > whether we should force this behavior on users even if their
> > preference is not to.)
> 
> VC is intended to provide a unified interface across backends, even if 
> it's at times different from the "native" behaviors.
> 
> Anyway, it's very easy to get the names against the root anyway: just 
> open VC-Dir there. And it's the default input: M-x vc-dir RET.

OK.