twDisplay( wHndl )
 ----------------------------------------------------------------------------
     Displays a window from the stack. If the window carries shadow
     information, it is updated for the current screen when it is
     displayed. Suggested use is on a SET KEY to redisplay previous
     information.

       Arguments:

     wHndl  -  'N' Level of the window to be displayed.

     wColor -  'C' Colour in which to display the window.

       Return:

     Current window handle.

       Example:

     WIN2 := twOpen( 5, 5, 20, 45, "GR+/R", 3, 2 )
     WIN3 := twOpen( 12, 24, 16, 68, "W+/B", 7, 2 )
     WIN4 := twOpen( 2, 49, 22, 63, "GR+/G", 9, 2 )
     INKEY( .2 )
     twDisplay( WIN3 )
     INKEY( .2 )
     twDisplay( WIN2 )