pgsql: Fix corner case where SELECT FOR UPDATE could return a row twice

Fix corner case where SELECT FOR UPDATE could return a row twice.

In READ COMMITTED mode, if a SELECT FOR UPDATE discovers it has to redo
WHERE-clause checking on rows that have been updated since the SELECT's
snapshot, it invokes EvalPlanQual processing to do that.  If this first
occurs within a non-first child table of an inheritance tree, the previous
coding could accidentally re-return a matching row from an earlier,
already-scanned child table.  (And, to add insult to injury, I think this
could make it miss returning a row that should have been returned, if the
updated row that this happens on should still have passed the WHERE qual.)
Per report from Kyotaro Horiguchi; the added isolation test is based on his
test case.

This has been broken for quite awhile, so back-patch to all supported
branches.

Branch
------
REL9_1_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/21946ac9b61bbd3257449ce7ad511618e1a5d695

Modified Files
--------------
src/backend/executor/nodeLockRows.c |   22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)