OTS — Clarification of set_response behaviour

The Activity service specification states, in the description of
the SignalSet::set_response method:
"The SignalSet returns a boolean to indicate whether or not the
Action that returned the response should be informed of any further
signals from this signal set; if the value is true then the Action
continues to receive Signals."

This suggests that, if the SignalSet is used to broadcast signals
(rather than simply produce completion signals), an Action that
indicated it required no further signals during the first broadcast
within a particular Activity may well expect to receive signals if
the SignalSet was requested to broadcast a second time within the
same activity or indeed was subsequently asked to produce completion
signals.

In a subordinate node, there is no knowledge from one
process_signal(Signal) to the next as to which particular broadcast
the signal comes from. Therefore, the subordinate has no way of
knowing whether a registered Action that indicated no-further-signals
on a previous set_response should receive signals on subsequent
process_signal calls from the superior.

see above