- parent transactions weren't started on the connection when adding a connection...

- parent transactions weren't started on the connection when adding a connection to a nested session transaction.
- session.transaction now always refers to the innermost active transaction, even when commit/rollback are called directly on the session transaction object.
- when preparing a two-phase transaction fails on one connection all the connections are rolled back.
- two phase transactions can now be prepared.
- session.close() didn't close all transactions when nested transactions were used.
- rollback() previously erroneously set the current transaction directly to the parent of the transaction that could be rolled back to.
- autoflush for commit() wasn't flushing for simple subtransactions.