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

[Stefan Monnier]

> users should complain more.  :-)

We make customization too easy.
Same with ELisp packages: it's too easy to work around a problem with
some `fboundp` or `condition-case` duct-tape, so the package authors
aren't encouraged to report problems to us (especially since even if we
fix the problem, they'll still need the duct-tape until our fix
trickles down to all their users).


        Stefan