[SDL] Beeps and bells.

[Mattias Engdegård]

>Yes, it has. See "man XBell" and "man XChangeKeyboardControl" (same page
>actually) for more info.

note that X11 server support for XBell() has traditionally been very poor.
for example this XSun uses the keyboard beeper, which can emit beeps of
varying duration at a fixed frequency carefully adjusted to be as
annoying to the human ear as possible

in other words, don't trust XBell and the less it is used the better