pgsql: Make RLS work with UPDATE ... WHERE CURRENT OF

Make RLS work with UPDATE ... WHERE CURRENT OF

UPDATE ... WHERE CURRENT OF would not work in conjunction with
RLS. Arrange to allow the CURRENT OF expression to be pushed down.
Issue noted by Peter Geoghegan. Patch by Dean Rasheed. Back patch
to 9.5 where RLS was introduced.

Branch
------
REL9_5_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/7d4240d6cd91d83d263a45501cc2f44fb1d0a537

Modified Files
--------------
src/backend/optimizer/path/allpaths.c     |   40 +++++++++++
src/backend/optimizer/util/clauses.c      |   10 +++
src/test/regress/expected/rowsecurity.out |  107 +++++++++++++++++++++++++++++
src/test/regress/sql/rowsecurity.sql      |   49 +++++++++++++
4 files changed, 206 insertions(+)