bug#50572: 28.0.50; [PATCH] fix VC to find the responsible backend with the most specific path.

[Eli Zaretskii]

> From: Manuel Giraud <manuel@ledu-giraud.fr>
> Cc: 50572@debbugs.gnu.org
> Date: Tue, 14 Sep 2021 17:15:14 +0200
> 
> > It didn't work for me, either.  Which is a pity, since the manual says
> > it should.  I guess we lost this at some point; patches to fix that
> > are welcome.
> 
> FTR, I don't if it was lost at some point because reading the code it
> seems that prefix is taken into account if the file is already
> registered into some backend… but for unregistered file it seems that
> nothing is done with the prefix.

So maybe this never worked for registering, in which case I think it
would be good to add that.  Because the manual says this should work
for "C-x v v" in general, not just under some conditions.  And what's
the most natural occasion to determine the backend if not when you
register a file?