bug#6953: 24.0.50; serious security bug in create backup files

[Eli Zaretskii]

> From: Glenn Morris <rgm@gnu.org>
> Date: Thu, 02 Sep 2010 01:38:42 -0400
> Cc: 6953@debbugs.gnu.org
> 
> A partial solution for the first problem is simple (below).

Note that this partial solution will do nothing on MS-Windows.
(There's currently no infrastructure in Emacs to create _really_
private files and directories on MS-Windows, even on filesystems that
support file security.)