bug#31039: 27.0.50; allow silencing auto-save

[Eli Zaretskii]

> Date: Sat, 11 Aug 2018 12:31:34 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: 31039-done@debbugs.gnu.org, npostavs@gmail.com, aaronjensen@gmail.com
> 
> A few minor nits for your future contributions:
> 
>   . For changes in the manuals, the name of the node where the change
>     is done should be mentioned in parentheses, as if it were a
>     function.
>   . Please make sure the NEWS entries are filled according to the
>     default setting of fill-column (use M-q to do that).
>   . It is preferable to explicitly mention the new functions/variables
>     in the log entries for NEWS and the manuals.

Sorry, 2 more:

  . Always mention the bug number in the log entry.
  . When you add a new customizable option, always mark it with the
    first Emacs version where the option will appear, in this case
    27.1.

Thanks.