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

[Stefan Kangas]

Stefan Kangas <stefan@marxist.se> writes:

> So if we make that change, perhaps we should make `ding' obsolete in
> favour of `user-error'.

Or maybe not: `ding' cancels keyboard macros, right?  So there would
still be some use for it, if you want to cancel a keyboard macro but do
nothing visible in interactive use.