Add support for SDL audio. Deiver order attempted for audio output is now

as follows:

SDL -> Win32 wave mapper -> ALSA -> OSS -> Win32 Beep() -> unix_beep()

Issues are as follows:
SDL requires SDL.dll/libSDL.so
Win32 wave mapper has a larget (~ .5 sec) delay between beeps on at least
Windows 2000 (possibly 9x and NT too)
ALSA Is completely untested.
OSS works fine (best tested)  ;-)
Beep() repeatedly plays the default beep wave on 9x.
unix_beep() is succeptable to various permissions problems.