Instead of trying to force WHERE clauses into CNF or DNF normal form,

Instead of trying to force WHERE clauses into CNF or DNF normal form,
just look for common clauses that can be pulled out of ORs.  Per recent
discussion, extracting common clauses seems to be the only really useful
effect of normalization, and if we do it explicitly then we can avoid
cluttering the qual with partially-redundant duplicated expressions, which
was an unpleasant side-effect of the old approach.