System V and Xenix compatibility

[Peter Fischman]

	I recently came off a project that ported a DOS application,
	Lotus 1-2-3 (you may have heard of it), to System V and Xenix.
	We developed on 386/ix and used gcc and gmake.  The executable
	runs on 386/ix, SCO Unix SysV.3.2, SCO Xenix386 2.3.2, AT&T
	Unix SysV.3.2, and AT&T Unix SysV.4.  The only part of the code
	that cares about the flavor of the OS is the video driver.  The
	SCO video interface is different from 386/ix and AT&T.  That's
	not much, in retrospect.