bug#31039: 27.0.50; allow silencing auto-save

[Eli Zaretskii <eliz@gnu.org>]

> From: Federico <federicotedin@gmail.com>
> Date: Mon, 6 Aug 2018 20:02:28 -0300
> Cc: Noam Postavsky <npostavs@gmail.com>, Aaron Jensen <aaronjensen@gmail.com>, 31039@debbugs.gnu.org
> 
> Noam, Eli: I've applied the fixes you have both mentioned. I ended up
> using DEFVAR_BOOL to create the variable, but I'm not sure I used the
> variable correctly when calling Fdo_auto_save (the function only takes
> Lisp_Object). I have attached a new patch.
> 
> Regarding the copyright assignment, mine was approved one or two weeks ago.

Thanks, pushed to the master branch.

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.

You can look at the changes I actually pushed to see how I handled
those issues in this commit.

Thank you for your contribution; your copyright assignment is now on
file.