ModeShape managed transactions can cause NPEs if they're rolled back after a failed commit

ModeShape attempts to roll-back transactions whenever an unexpected exception is caught during a session save or during one of the operations executed at repository startup.

When using ModeShape managed transactions, if such a transaction throws an exception during tx.commit, depending on the case (see linked issue for an example) some other party (most notably AS or ISPN) can rollback the transaction in response.

If that is the case, ModeShape should not attempt to rollback the transaction again (which will fail) because this will hide the original cause of the failure. In such cases, ModeShape should make sure the original exception (which triggered the rollback in the first place) is sent back to the caller.