bug#21816: elisp-mode-tests fails on a case-preserving filesystem

[Eli Zaretskii <eliz@gnu.org>]

> From: Alexis <flexibeast@gmail.com>
> Date: Wed, 04 Nov 2015 16:24:27 +1100
> Cc: Juanma Barranquero <lekktu@gmail.com>, 21816@debbugs.gnu.org,
> 	Dmitry Gutov <dgutov@yandex.ru>
> 
>     I did not try a non-ASCII file name; I'm not sure how to construct one that has a non-ASCII casing issue. 
> 
> Perhaps use German Eszett / sharp S / Unicode LATIN SMALL LETTER SHARP S? The words 'Strasse' and 'Straße' are equivalent, but typically the latter is up-cased to 'STRASSE', rather than 'STRAẞE'. (Indeed, LATIN CAPITAL LETTER SHARP S was only added to Unicode in version 5.1.) In turn, 'STRASSE' is typically down-cased to 'strasse'. Further, even the latest version of Unicode notes that SpecialCasing.txt doesn't handle this situation: 

Thanks for bringing up this problematic issue.  However, this issue is
not relevant to file names, at least not on MS-Windows, because
Windows doesn't consider this case conversion either:

  (file-exists-p "Straße.txt")
   => t
  (file-exists-p "straße.txt")
   => t
  (file-exists-p "STRAßE.TXT")
   => t
  (file-exists-p "STRASSE.txt")
   => nil