SocketPipe shouldn't close the socket.

This is a layering violation - the SocketPipe doesn't own
the socket and provides no other way to close the socket, leading
to unnecessary complexity like that in interface.py.

I looked at deamon.py and NetworkProxy - the two other users,
and they don't close the sockets explicitly, just let them be
garbage collected.

lib/util.py

@@ -360,8 +360,7 @@ class SocketPipe:
                 traceback.print_exc(file=sys.stderr)
                 data = ''
 
-            if not data:
-                self.socket.close()
+            if not data:  # Connection closed remotely
                 return None
             self.message += data
             self.recv_time = time.time()