advanced sound options menu. Removed opl_enable from the menu.
- Added OPL synth as MIDI device -3. Since this is based on the MUS player
code, it only supports those events and controllers supported by MUS.
Some of Duke's MIDIs sound awful, but I think that may be more because
it's using different instruments... There's a thread in the MIDI streamer
class that could be taken out for Linux, since it doesn't need to deal
with the Windows Multimedia API, but for now, this is still Windows-only.
SVN r864 (trunk)
