Add window_activity format, from Thomas Adam based on a diff originally

from propos6 at gmail dot com.

input.c

@@ -20,6 +20,7 @@
 
 #include <stdlib.h>
 #include <string.h>
+#include <time.h>
 
 #include "tmux.h"
 
@@ -849,6 +850,9 @@ input_parse(struct window_pane *wp)
 	wp->window->flags |= WINDOW_ACTIVITY;
 	wp->window->flags &= ~WINDOW_SILENCE;
 
+	if (gettimeofday(&wp->window->activity_time, NULL) != 0)
+		fatal("gettimeofday failed");
+
 	/*
 	 * Open the screen. Use NULL wp if there is a mode set as don't want to
 	 * update the tty.