Change in porting tactics: OS/2's EMX porting layer doesn't allow multiple

Change in porting tactics: OS/2's EMX porting layer doesn't allow multiple
threads to call select() simultaneously.  So, it's time to do a real, live,
native OS/2 port.  See defines for __EMX__ (the porting layer) vs. __OS2__
(native). Both versions will work, but using __OS2__ offers multi-threading.