By closing a session when the new MINA inputClosed() handler is triggered, we run
the risk of sending data to the peer. As that peer is known to be dead, this is
pointless (and potentially dangerous - deadlocks have been observed that are likely
related to this scenario).

To prevent sending data during session closure, the close() method has been
overloaded with an argument that indicates if the peer is known to be dead. When
set, its implementation will not attempt to send data.