Remember last pane or type of location for double and triple clicks and

correctly handle it changes between first and second or second and
third. GitHub issue 4795 from Shaobo Song.

tmux.h

@@ -1942,6 +1942,8 @@ struct client {
 	struct event		 repeat_timer;
 
 	struct event		 click_timer;
+	int			 click_where;
+	int			 click_wp;
 	u_int			 click_button;
 	struct mouse_event	 click_event;