Fix race conditions in {tcp,ipc}_connecter

Once the object has been terminated, it is unsafe for this object
to refer to its parent.

The bug was responsible for occasional
test_shutdown_stress failures.

src/tcp_connecter.hpp

@@ -53,6 +53,7 @@ namespace zmq
 
         //  Handlers for incoming commands.
         void process_plug ();
+        void process_term (int linger_);
 
         //  Handlers for I/O events.
         void in_event ();