pgsql: Fix incorrect checking of deferred exclusion constraint after a

Fix incorrect checking of deferred exclusion constraint after a HOT update.

If a row that potentially violates a deferred exclusion constraint is
HOT-updated later in the same transaction, the exclusion constraint would
be reported as violated when the check finally occurs, even if the row(s)
the new row originally conflicted with have since been removed. This
happened because the wrong TID was passed to check_exclusion_constraint(),
causing the live HOT-updated row to be seen as a conflicting row rather
than recognized as the row-under-test.

Per bug #13148 from Evan Martin. It's been broken since exclusion
constraints were invented, so back-patch to all supported branches.

Branch
------
REL9_0_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/b93c8eaf8c35485175358c552cd5adce0e197ec9

Modified Files
--------------
src/backend/commands/constraint.c | 17 +++++++++++------
src/test/regress/input/constraints.source | 10 ++++++++++
src/test/regress/output/constraints.source | 14 ++++++++++++++
3 files changed, 35 insertions(+), 6 deletions(-)