Revert "Remove the extra outpipe handling as the session is quite capable of delaying the creation of the pipe until the connection has happened. Simply don't build the pipe, and let it do that automatically."

This reverts commit 06485d9200.

src/session_base.hpp

@@ -106,7 +106,10 @@ namespace zmq
 
         //  Pipe connecting the session to its socket.
         zmq::pipe_t *pipe;
-        
+
+        //  Pipe connecting the socket to the client
+        zmq::pipe_t *outpipe;
+
         //  This flag is true if the remainder of the message being processed
         //  is still in the in pipe.
         bool incomplete_in;