OTS — failure assumption

The current draft of the Activity Service implicitly assumes a "presumed abort" type protocol, but doesn't mention it explicitly. The only reference an Action has to the activity it is involved with is the ActivityCoordinator it registered with. Now, if that coordinator is defunct (e.g., it failed before termination or simply decided to "abort" and couldn't get through to the Action because it had failed) when the Action calls get_status it will presumably get an OBJECT_NOT_EXIST exception. The Action should use this as an indication of a roll back, and act accordingly.

Add a Failure Assumptions subsection in the Implementor's View