Reverted to a simpler shutdown. This seems to disconnect and reconnect the pipe properly, but there is a problem in overall shutdown when the pipe has blocked and reconnected - the session seems to get terminated() called on it only in shutdown for the original pipe, by which point it has been replaced. I am not sure at the moment why this only happens then, but this does mean this patch is broken at the moment

src/session_base.hpp

@@ -103,9 +103,6 @@ namespace zmq
 
         //  Pipe connecting the session to its socket.
         zmq::pipe_t *pipe;
-        
-        //  Socket end of the pipe, for delay attach scenario
-        zmq::pipe_t *outpipe;
 
         //  This flag is true if the remainder of the message being processed
         //  is still in the in pipe.