[Reviewer] Fix to Sprout issue174

Matt

Can you this fix please.  I decided that the activesock layer was the best place for a fix along the lines we discussed yesterday - the pj_activesock_close function is nicely idempotent and immediately removes the socket from the IO queue.  I look at fixing it higher up (in the TCP transport) as well, but it would have been very fiddly.

I've tested it by running it in the scenario that was consistently failing yesterday.  I no longer see the lock up and I haven't seen any other instability either.

Mike