bug#49918: 28.0.50; cd function expands CDPATH incorrectly

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: phil@hagelb.org,  49918@debbugs.gnu.org
> Date: Sun, 08 Aug 2021 14:42:46 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > Why does the current implementation of parse-colon-path use
> > expand-file-name?  The comment says "to expand "~", but the original
> > implementation in Emacs 27 didn't do that.
> 
> I should probably have written (etc) after that comment...
> 
> > Bug#21454 only wanted to avoid mis-interpreting duplicate slashes in
> > the input path, but there's no need to collapse them, so I don't see
> > how the call to expand-file-name is at all necessary, and could
> > potentially change behavior in unintended ways.  Am I missing
> > something?
> 
> Tino's tests in files-tests-bug-21454 test explicitly for the duplicate
> slash collapsing, so I assumed that was part of the point.  But I may
> well be mistaken -- feel free to adjust this some more.

Done.  I don't think we should collapse slashes except the leading
one, it isn't something this function should do, and is not in its
documentation.