Referencing NULL pointers

[Guy Harris]

>In retrospect I think we probably should have gone the other way on this;
>or at provided a way to test code with different behaviour.

Yes.  The paged versions of System V from AT&T - the VAX one for sure,
and probably the 3B2 one as well, at least - have a "-z" flag that tells
the linker to create an image with no page zero.  Unfortunately, it's
not the default, which means there's still a fair bit of sloppy code in
S5R3, but at least you do have the choice of enforcing correct behavior.