bug#18891: Doesn't handle pwd = /C: very well

[Eli Zaretskii]

> From: Michael Albinus <michael.albinus@gmx.de>
> Cc: Stefan Monnier <monnier@iro.umontreal.ca>,  Eli Zaretskii <eliz@gnu.org>, 
>  18891@debbugs.gnu.org
> Date: Fri, 07 Nov 2014 15:52:37 +0100
> 
> >    C-x C-f bar RET
> >
> > since it again tries to do something via Tramp and fails.
> 
> This shall work now, both cases bar being an existing file, and bar not
> existing. I've committed respective patches to the emacs-24 branch.

Your change calls Ffile_accessible_directory_p, Fstring_match, and
Fsubstring with a unibyte (encoded) string as their argument.  I think
we should avoid that, as, e.g., Fstring_match might yield a false
positive under some encodings.