>># 
>># Copyright 1990, 1991 by the Massachusetts Institute of Technology and
>># UniSoft Group Limited.
>># 
>># Permission to use, copy, modify, distribute, and sell this software and
>># its documentation for any purpose is hereby granted without fee,
>># provided that the above copyright notice appear in all copies and that
>># both that copyright notice and this permission notice appear in
>># supporting documentation, and that the names of MIT and UniSoft not be
>># used in advertising or publicity pertaining to distribution of the
>># software without specific, written prior permission.  MIT and UniSoft
>># make no representations about the suitability of this software for any
>># purpose.  It is provided "as is" without express or implied warranty.
>># 
>># $XConsortium: cnnctnnmbr.m,v 1.6 92/06/11 15:56:25 rws Exp $
>># 
>>#
>>TITLE ConnectionNumber CH02
>>ASSERTION D ConnectionNumber-1
If the system is POSIX compliant: A call to
ConnectionNumber returns the file descriptor of the display
specified by the display argument. Otherwise: A call to
ConnectionNumber returns the connection number of the
display specified by the display argument.
>>STRATEGY
If the system is POSIX compliant:
  Open a display using XOpenDisplay.
  Create a child process.
  In Child :
    Set IOErrorHandler to an errorhandler function which exits immediately.
    Obtain the connection number of the display using ConnectionNumber.
    Close the connection using close.
    Perform a XNoOp request on the display.
    Flush the O/P using using XFlush.
  In parent:
    Obtain child's exit status.
    Verify that the child exited from the error handler.
Otherwise:
  UNTESTED
