add regression tests for divide-by-zero

Neil Conway <neilc@samurai.com> writes:

I've noticed a couple platforms / compiler combinations having problems
with properly handling divide-by-zero errors, so this patch updates the
regression tests to include this behaviour. I also took the liberty of
updating some Postquel terms their SQL equivalents (e.g. retrieve ->
select, etc.)

Applied along with code patches to make sure the behavior will be
uniform across platforms.

regards, tom lane