pgsql: Always require SELECT permission for ON CONFLICT DO UPDATE.

Always require SELECT permission for ON CONFLICT DO UPDATE.

The update path of an INSERT ... ON CONFLICT DO UPDATE requires SELECT
permission on the columns of the arbiter index, but it failed to check
for that in the case of an arbiter specified by constraint name.

In addition, for a table with row level security enabled, it failed to
check updated rows against the table's SELECT policies when the update
path was taken (regardless of how the arbiter index was specified).

Backpatch to 9.5 where ON CONFLICT DO UPDATE and RLS were introduced.

Security: CVE-2017-15099

Branch
------
REL9_6_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/1f23d1cd21ed46dba882729bedd9c40b71995989

Modified Files
--------------
src/backend/catalog/pg_constraint.c | 98 +++++++++++++++++++++++++++++++
src/backend/parser/parse_clause.c | 21 ++++++-
src/backend/rewrite/rowsecurity.c | 20 ++++++-
src/include/catalog/pg_constraint_fn.h | 2 +
src/test/regress/expected/privileges.out | 16 ++++-
src/test/regress/expected/rowsecurity.out | 15 ++++-
src/test/regress/sql/privileges.sql | 19 +++++-
src/test/regress/sql/rowsecurity.sql | 14 ++++-
8 files changed, 194 insertions(+), 11 deletions(-)