From: David Hartwig <daybee@bellatlantic.net>

I put some extra checks to make sure a query was a good candidate for
rewrite into a UNION.    Besides the existing checks:

1.  Make sure the AND/OR tree was rectangular.  ( i.e.    3 X 4  or 10 X
3)
2.  Only one table.
3.  Must have an AND dimension.
4.  At least 9 OP expressions total

Also  cleaned up and commented.