commandserver: close server's fds explicitly from a worker

The forked worker does not need to accept connections from the server's
socket fd. So let's just close them explicitly to avoid surprises.

Differential Revision: https://phab.mercurial-scm.org/D3720

mercurial/commandserver.py

@@ -494,6 +494,8 b' class unixforkingservice(object):'
                     conn.close()  # release handle in parent process
             else:
                 try:
+                    selector.close()
+                    self._sock.close()
                     self._runworker(conn)
                     conn.close()
                     os._exit(0)