actions prior to malfunction cannot be cancelled

A competitor grumbled that an action sent to an agent before it malfunctioned, would always be performed after the malfunction completed. Erik has commented that some actions do have this semantic, eg turning, because the "points" at a junction may already be set. However there is a case for allowing an agent to issue a "stop", prior to resumption of power. We would then need to implement something to remember that the agent is committed to turning left, travelling forward, etc.