bug#30215: Visiting files from zip archives should not modify directory time

[Eli Zaretskii]

> From: Juri Linkov <juri@linkov.net>
> Cc: 30215@debbugs.gnu.org
> Date: Sat, 27 Jan 2018 23:16:20 +0200
> 
> >> Creation of a backup file is not a problem, because backups are created
> >> on saving.
> >
> > What about auto-saving in general, and the new auto-save-visited-mode
> > in particular?
> 
> The default value of `auto-save-visited-interval' is 5 seconds, but the
> time of extracting a file from the archive is measured in microseconds.

"Microseconds"?  Does that include very large files? what about
archives on remote machines?

> BTW, while looking at `auto-save-visited-mode', I noticed that the
> docstring of `save-some-buffers' could be improved:

Fixed, thanks.