bug#27982: 25.1.50; expand-file-name docstring on how to traverse the filesystem

[Eli Zaretskii]

> From: Nicolas Richard <youngfrog@members.fsf.org>
> Cc: 27982@debbugs.gnu.org
> Date: Wed, 23 Aug 2017 14:18:24 +0200
> 
> (let ((dirname current-directory))
>    (format "%s versus %s"
>       (directory-file-name (file-name-directory dirname))
>       (expand-file-name ".." dirname)))
> => "/home/youngfrog versus /home"
> => Effect is clearly different.

Crystal ball says that current-directory (which you probably meant to
be default-directory instead) ends in a slash, in which case remove
it, and the 2 results will match.