FUML13 — SendSignalAction completion semantics

SendSignalAction completion semantics. SendSignalAction shouldn't require the event pool to be updated before the action completes.

Add active behavior to EventOccurrence

Adding an event occurrence into the event pool of the target should always be done in a separate execution thread than that of the sender of the event occurrence. Not only does this better model the asynchronous nature of signal sends, it also better models the semantics of inter-object communication in general, as discussed in 2.4 Genericity of the Execution Model, even for, say, call event occurrences. That is because the semantics of concurrency in fUML allows for arbitrary sequential or parallel ordering of the execution of concurrent behaviors. Therefore, having concurrent threads for actually sending each event occurrence to the target better models the possibility that concurrent sends may be arbitrarily re-ordered, or even potentially lost (if the execution of a send behavior ends up being postponed, say, until sequentially after its target object has been destroyed).