Fix problems with window sizing seen by Raghavendra D Prabhu when

starting tmux from .xinitrc.

One of the very few things the server relies on the client for now is to
pass through a message on SIGWINCH, but there is a condition where
potentially a SIGWINCH may be lost during the transition from unattached
(main.c) to attached (client.c). So trigger a size change immediately
after the client installs its SIGWINCH handler.

Also, when the terminal is resized, reset the scroll region and cursor
position. Previously, we were clearing our saved idea of these, but in
fact some terminals do not reset them on resize, so this caused problems
during redraw.

While here make a resize to the same size not cause a redraw and rename
the tmux.out output log file to include the tmux PID.

client.c

@@ -175,6 +175,13 @@ client_main(void)
 	/* Set up signals. */
 	set_signals(client_signal);
 
+	/*
+	 * Send a resize message immediately in case the terminal size has
+	 * changed between the identify message to the server and the MSG_READY
+	 * telling us to move into the client code.
+	 */
+	 client_write_server(MSG_RESIZE, NULL, 0);
+
 	/*
 	 * imsg_read in the first client poll loop (before the terminal has
 	 * been initialised) may have read messages into the buffer after the