pgsql: Fix ON CONFLICT DO UPDATE for tables with oids.

Fix ON CONFLICT DO UPDATE for tables with oids.

When taking the UPDATE path in an INSERT .. ON CONFLICT .. UPDATE tables
with oids were not supported. The tuple generated by the update target
list was projected without space for an oid - a simple oversight.

Reported-By: Peter Geoghegan
Author: Andres Freund
Backpatch: 9.5, where ON CONFLICT was introduced

Branch
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REL9_5_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/90586ef127c593002897ee0bcafdf2adb6a18c7d

Modified Files
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src/backend/executor/nodeModifyTable.c        |    2 +-
src/test/regress/expected/insert_conflict.out |   59 +++++++++++++++++++++++++
src/test/regress/sql/insert_conflict.sql      |   22 +++++++++
3 files changed, 82 insertions(+), 1 deletion(-)