The proposes join removal patch for upcoming PostgreSQL v8.5 replaces outer 
join by inner one when the condition matches with foreign key constraint, 
because it assumes here is one or more outer tuples due to FK constraint.
But this assumption is not correct when row-level security is available on 
the target relations, so we have to add a check whether row-level security 
is available on either of relations, or not.

Maybe, it can be possible by checking tuple_perms != 0.