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
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/b26e3d660df51a088d14c3c2cfce5990c13c1195

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(+)