Attempts to fix segfaults noted in issue #11

This will actually behave quite differently to the subscriber cell. The subscriber cell has a latency of `40*5 = 200msec` before it passes control (via DO_OVER) to the scheduler. The usual use case means that this imposes a 200ms latency before the scheduler can proceed to shutdown a plasm because of an external CTRL-C or similar.

Here this will impose up to an `n*40*200 ms` latency before the scheduler gets a chance to act.