Modified handling of exceptions in order to only back out relevant events. Specifically, network exceptions do not back out all events. If caught, exceptions do not back out of any events, and instead the event in which the exception occurred is allowed to complete and commit. To do this, I modified _raise_network_exception to go through each active event and only notify events which have communicated with the partner endpoint by putting a network failure result in their queue. If a network or application exception is not caught then the event is backed out and the exception is raised (thus it is propogated out to the caller).