bug#38453: Error out if dumping while interactive?

[Eli Zaretskii]

> From: Philipp Stephani <p.stephani2@gmail.com>
> Date: Mon, 23 Dec 2019 21:14:33 +0100
> Cc: Kévin Le Gouguec <kevin.legouguec@gmail.com>, 
>       38453-done@debbugs.gnu.org
> 
> > I think it's misguided, since we intend to lift this limitation in
> > some future release.
> 
> If and when we lift it, we can remove the error again.

Given the error message, people will think it's a limitation that
cannot be easily removed, so the chances of its being removed are much
lower, especially a few years from now.