bug#27986: 26.0.50; 'rename-file' can rename files without confirmation

[Eli Zaretskii]

> Cc: Eli Zaretskii <eliz@gnu.org>, 27986@debbugs.gnu.org
> From: Paul Eggert <eggert@cs.ucla.edu>
> Date: Mon, 14 Aug 2017 16:03:13 -0700
> 
> Philipp Stephani wrote:
> 
> > there's no way to special-case
> > casing changes while keeping atomicity intact. So I'd rather have Emacs
> > react conservatively and skip the casing check entirely.
> 
> Yes, that makes sense, at least for macOS.

As I wrote, we should not lose the feature that renaming a file on
macOS to a different letter-case works without nagging the user with
confirmations.  I don't think this runs afoul of security, since the
letter-case check doesn't break atomicity in any way.