Is there a good reason that Sys.sigint is blocked when I compile a native
application under Cygwin using threads?  Is O'Caml doing the blocking or 
 Cygwin?  I would like to develop a service using cygrunsrv to run  it, but that
 requires my application to take a signal when killed.  Is it safe to unblock any
 signals when using threads under Cygwin?  If so, which one's.