Ensure that all places that are complaining about exhaustion of shared

Ensure that all places that are complaining about exhaustion of shared
memory say 'out of shared memory'; some were doing that and some just
said 'out of memory'.  Also add a HINT about increasing max_locks_per_transaction
where relevant, per suggestion from Sean Chittenden.  (The former change
does not break the strings freeze; the latter does, but I think it's
worth doing anyway.)