bug#26911: 25.2; eshell "cd .." doesn't work correctly with TRAMP

[Eli Zaretskii]

> Date: Fri, 28 Aug 2020 10:01:43 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: 26911@debbugs.gnu.org, mattiase@acm.org, michael.albinus@gmx.de,
>  yegortimoshenko@gmail.com
> 
> I've now fixed most of the failures, but one still remains, and it
> definitely seems to be due to the latest changes in expand-file-name,
> note the "c:." part below:

This is one symptom of a more general (and much more serious) problem
with the modified expand-file-name:

  (expand-file-name "d:/foo/bar/../baz") => "d:./foo/baz"

That period after the colon following the drive letter shouldn't be
there.  As you may imagine, many Emacs commands are now broken because
of this.  This must be fixed ASAP.