pgsql: Ensure tableoid reads correctly in EvalPlanQual-manufactured tup

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.

Branch
------
REL9_1_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/4a4fd2b0ceedb339118b0cf10ca78e472ce20a90

Modified Files
--------------
src/backend/executor/execMain.c |    4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)