Add dialog cleanup after dialplan callback finshed

[vodik]

I need to do a bit more research into how this should be implemented to be SIP compliant, but something sensible needs to happen to inbound traffic on a dialog after the server has stopped processing traffic on that dialog.

Currently the traffic is ignored (its queued, but the queue is not being read from anymore).

One of two things could happen, not sure which one makes sense (leaning on 2)

1. Reject the traffic with some sort of error message.
2. Call the dialplan handler again, and do something to make it re-entrant, so the server can pick up where is stopped.

[ovv]

With #113 the application completely discard the dialplan once they are closed so inbound traffic on an old dialog goes through the Dialplan again and it is recreated.