url: fix https client authentication through proxy

There is no tests for this, but the parameter order was obviously wrong.

mercurial/url.py

@@ -540,8 +540,8 b' if has_https:'
                 self.sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
                 self.sock.connect((self.host, self.port))
                 if _generic_proxytunnel(self):
-                    self.sock = _ssl_wrap_socket(self.sock, self.cert_file,
-                                                 self.key_file)
+                    self.sock = _ssl_wrap_socket(self.sock, self.key_file,
+                            self.cert_file)
             else:
                 BetterHTTPS.connect(self)