Sound support enabled on Cygwin

[Ken Brown]

In bzr revision 117968 on the trunk I enabled sound support on Cygwin. 
I gave it only minimal testing, by evaluating

  (play-sound-file "/cygdrive/c/Windows/Media/chimes.wav")

If any Cygwin users know how to test it more rigorously, please do so 
and report any bugs.

Thanks.

Ken