- New command display-message (alias display) to display a message in the

status line (bound to "i" and displays the current window and time by
  default). The same substitutions are applied as for status-left/right.
- Add support for including the window index (#I), pane index (#P) and window
  name (#W) in the message, and status-left or status-right.
- Bump protocol version.

From Tiago Cunha, thanks!

window.c

@@ -379,6 +379,21 @@ window_pane_at_index(struct window *w, u_int idx)
 	return (NULL);
 }
 
+u_int
+window_pane_index(struct window *w, struct window_pane *wp)
+{
+	struct window_pane	*wq;
+	u_int			 n;
+
+	n = 0;
+	TAILQ_FOREACH(wq, &w->panes, entry) {
+		if (wp == wq)
+			break;
+		n++;
+	}
+	return (n);
+}
+
 u_int
 window_count_panes(struct window *w)
 {