bug#31039: 27.0.50; allow silencing auto-save

[Eli Zaretskii]

> From: Noam Postavsky <npostavs@gmail.com>
> Date: Sun, 05 Aug 2018 22:43:16 -0400
> Cc: aaronjensen@gmail.com, 31039@debbugs.gnu.org
> 
> > +  DEFVAR_LISP ("auto-save-quiet", auto_save_quiet,
> > +          doc: /* Non-nil means do not print any message when auto-saving. 
> > */);
> > +  auto_save_quiet = Qnil;
> 
> The C name of the variable should start with V, like the others.

For a boolean variable, one can use DEFVAR_BOOL, in which case the
"start with V" nuisance can be avoided (and the code will be a tad
more efficient, too).