Broken lock management in policy.c.

CREATE POLICY takes AccessExclusiveLock on the table a policy is being
added to -- good -- and then releases it when done -- bad. Correct
behavior is to hold the lock till commit, because otherwise there is
no guarantee that other backends will see the updated catalog rows in
time, or indeed at all.

The same goes for ALTER POLICY, and possibly DROP POLICY (I've not
found the implementation of that ...)

If we fix this, I believe we could also remove the weasel wording that was
added to create_policy.sgml in commit 43cd468cf01007f3 about how the
system might transiently fail to enforce row security correctly.

regards, tom lane