pgsql: Fix bogus lock release in RemovePolicyById and RemoveRoleFromObj

Fix bogus lock release in RemovePolicyById and RemoveRoleFromObjectPolicy.

Can't release the AccessExclusiveLock on the target table until commit.
Otherwise there is a race condition whereby other backends might service
our cache invalidation signals before they can actually see the updated
catalog rows.

Just to add insult to injury, RemovePolicyById was closing the rel (with
incorrect lock drop) and then passing the now-dangling rel pointer to
CacheInvalidateRelcache. Probably the reason this doesn't fall over on
CLOBBER_CACHE buildfarm members is that some outer level of the DROP logic
is still holding the rel open ... but it'd have bit us on the arse
eventually, no doubt.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/f47b602df80d7647ca2e71c86f7228b1bf5bf9f3

Modified Files
--------------
src/backend/commands/policy.c | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)