pgsql: Fix memory leak created by deferrable-index-constraints patches.

Log Message:
-----------
Fix memory leak created by deferrable-index-constraints patches.

We need to free the OID list returned by ExecInsertIndexTuples to avoid
a query-lifespan memory leak. When many rows require rechecking, this
can be a significant leak --- it's even more than the space used for the
queued trigger events.

Dean Rasheed

Modified Files:
--------------
pgsql/src/backend/commands:
copy.c (r1.321 -> r1.322)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/commands/copy.c?r1=1.321&r2=1.322)
pgsql/src/backend/executor:
nodeModifyTable.c (r1.4 -> r1.5)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/nodeModifyTable.c?r1=1.4&r2=1.5)