pgsql: Ensure that INSERT ...

Log Message:
-----------
Ensure that INSERT ... SELECT into a table with OIDs never copies row OIDs
from the source table. This could never happen anyway before 8.4 because
the executor invariably applied a "junk filter" to rows due to be inserted;
but now that we skip doing that when it's not necessary, the case can occur.
Problem noted 2008-11-27 by KaiGai Kohei, though I misunderstood what he
was on about at the time (the opacity of the patch he proposed didn't help).

Modified Files:
--------------
pgsql/src/backend/executor:
execMain.c (r1.322 -> r1.323)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/execMain.c?r1=1.322&r2=1.323)