Only do the automatic-rename dance if the pane has changed (seen output,

or new active pane).

tmux.h

@@ -826,6 +826,7 @@ struct window_pane {
 #define PANE_RESIZE 0x8
 #define PANE_FOCUSPUSH 0x10
 #define PANE_INPUTOFF 0x20
+#define PANE_CHANGED 0x40
 
 	int		 argc;
 	char	       **argv;