[CM] with-threaded-sound?

[Bill Schottstaedt]

Your form of that macro works great -- thanks! 

> I wonder if guile is one of the few scheme implementations, 
> (maybe  the only one except java-schemes such as SISC and kawa (?)), with 
> support for real threads. 

I got bogged down trying to figure this out -- I think Guile does
go to "real" threads, Gauche does not (I believe its threads are
repackaged call/cc's), and I can't tell yet what sbcl does.