bug#1305: All code that currently beeps should use visual bell instead

[Gregory Heytings]

> > and a new prettier bell function, which would be the default
>
> Another option would be to use your newer bell on MacOS (which has 
> universally negative feedback), but keep the current one on GNU/Linux 
> and Windows

IMO a default that gives the same result across platforms would be much 
better.  I'm not sure what you mean by "the current one on GNU/Linux and 
Windows": the current default is an audible bell.  If you mean "make the 
current visible-bell the default", I can only repeat that the visible bell 
on GNU/Linux is ugly.  Would you imagine such a behavior in Visual Studio, 
Sublime or Atom?

> Windows (maybe? very little has been said here about whether it's better 
> or worse).

I can't really say whether it's better or worse, with visible-bell t on 
Windows the frame briefly flashes (with the FlashWindow function), a bit 
like a flash in a terminal.  Among the three visible-bell t behaviors, 
it's the best one IMO, in the sense that it's visible and not intrusive. 
But I can't say it's nice.

> Which platform are you on, BTW?

Not sure this is relevant to the current discussion, but: 99% GNU/Linux 
(Debian), 0.95% macOS, 0.05% Windows.