Log Message:
-----------
Fix predicate-proving logic to cope with binary-compatibility cases when
checking whether an IS NULL/IS NOT NULL clause is implied or refuted by
a strict function. Per example from Dawid Kuroczko.
Backpatch to 8.2 since this is arguably a performance bug.
Modified Files:
--------------
pgsql/src/backend/optimizer/util:
predtest.c (r1.15 -> r1.16)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/optimizer/util/predtest.c.diff?r1=1.15&r2=1.16)