Ensure tableoid reads correctly in EvalPlanQual-manufactured tuples.

The ROW_MARK_COPY path in EvalPlanQualFetchRowMarks() was just setting
tableoid to InvalidOid, I think on the assumption that the referenced
RTE must be a subquery or other case without a meaningful OID.  However,
foreign tables also use this code path, and they do have meaningful
table OIDs; so failure to set the tuple field can lead to user-visible
misbehavior.  Fix that by fetching the appropriate OID from the range
table.

There's still an issue about whether CTID can ever have a meaningful
value in this case; at least with postgres_fdw foreign tables, it does.
But that is a different problem that seems to require a significantly
different patch --- it's debatable whether postgres_fdw really wants to
use this code path at all.

Simplified version of a patch by Etsuro Fujita, who also noted the
problem to begin with.  The issue can be demonstrated in all versions
having FDWs, so back-patch to 9.1.

src/backend/executor/execMain.c

@@ -2438,7 +2438,9 @@ EvalPlanQualFetchRowMarks(EPQState *epqstate)
 			/* build a temporary HeapTuple control structure */
 			tuple.t_len = HeapTupleHeaderGetDatumLength(td);
 			ItemPointerSetInvalid(&(tuple.t_self));
-			tuple.t_tableOid = InvalidOid;
+			/* relation might be a foreign table, if so provide tableoid */
+			tuple.t_tableOid = getrelid(erm->rti,
+										epqstate->estate->es_range_table);
 			tuple.t_data = td;
 
 			/* copy and store tuple */