bug#24441: 24.5; rename directory in dired to change case

[Eli Zaretskii]

> Cc: 24441@debbugs.gnu.org, schwab@suse.de, brady@bradyt.com
> From: Ken Brown <kbrown@cornell.edu>
> Date: Thu, 15 Sep 2016 12:03:08 -0400
> 
> > See the bug I pointed to, where John explained that OS X filesystems
> > can be either case-sensitive or case-insensitive.
> 
> FWIW, this is also true on Cygwin:
> 
>  
> https://cygwin.com/cygwin-ug-net/using-specialnames.html#pathnames-casesensitive

I was under the impression that most or all Cygwin users do use
case-sensitive file names.  Otherwise, quite a few packages that come
from Posix platforms will not work or mysteriously fail.

But if that's not the reality, then yes, a patch to add a run-time
test for Cygwin will also be welcome.