TRANS14 — SubtransactionAwareResource

Summary: if a SubtransactionAwareResource is registered with a subtransaction using
register_resource then according to the current specification it is "indirectly"
registered with the top-level transaction when the "subtransaction"s ancestors
have completed". In the transaction systems I have knowledge of which support
nested transactions, if the subtransaction or any of its parents rollback, then
any resources registered would be dropped, i.e., not propagated to the parent.