Add an extra boolean to 0-10 session to indicate closing

Based on discussion on list the 0-10 session open now negotiates back to a timeout of 0 no matter what it is requested to use, so the expiry should be changed to be a boolean representing whether to close the session immediately instead. It was suggested that an exception code be used to signal this, however since the close mechanism must be symmetric, and there are no suitable codes available in the 0-10 protocol specification, it was decided to retain the current mechanism of sessionRequestTimeout(0)/sessionTimeout(0) sessionDetach(name)/sessionDetached(name, NORMAL) command pairs, as this is what is suggested in s.3.6.4 of the specification.