bug#21652: bell chars

[Eli Zaretskii]

> From: Andreas Schwab <schwab@linux-m68k.org>
> Cc: Tom Baker <tombaker17@gmail.com>,  21652@debbugs.gnu.org,
>   stefan@marxist.se
> Date: Sun, 16 Aug 2020 19:51:20 +0200
> 
> > That sounds like a bug to me: Emacs should emulate what the shell does
> > outside of Emacs.
> 
> It's a matter of how much you want to do in the
> comint-output-filter-functions.

Right, so maybe we could have a function to handle the bell, and then
users who want it could customize comint-output-filter-functions to
include that function.