pgsql: Handle policies during DROP OWNED BY

Handle policies during DROP OWNED BY

DROP OWNED BY handled GRANT-based ACLs but was not removing roles from
policies.  Fix that by having DROP OWNED BY remove the role specified
from the list of roles the policy (or policies) apply to, or the entire
policy (or policies) if it only applied to the role specified.

As with ACLs, the DROP OWNED BY caller must have permission to modify
the policy or a WARNING is thrown and no change is made to the policy.

Branch
------
REL9_5_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/fda18e46a65196b98d6ca4ce4911085b0d2f182f

Modified Files
--------------
src/backend/catalog/pg_shdepend.c         |   13 ++
src/backend/commands/policy.c             |  256 +++++++++++++++++++++++++++++
src/include/commands/policy.h             |    2 +
src/test/regress/expected/rowsecurity.out |   14 ++
src/test/regress/sql/rowsecurity.sql      |   18 ++
5 files changed, 303 insertions(+)