[Reviewer Andy] Fix anti-looping in SproutletProxy so AIO node works

Andy

Can you review this fix for the AIO nodes, as per email discussion this morning.  I've updated the UTs to test this new behaviour, but I haven't run the AIO node yet - I was going to do this as part of re-cutting the release.

Mike
I think the old test was valid too (in particular it tests #741).  Please re-instate.