fixed bug #493385 - Cache headers not working with IE 5.5SP2

header.inc.php3

@@ -20,7 +20,7 @@ if ($cfgOBGzip) {
  */
 // Don't use cache (required for Opera)
 $now = gmdate('D, d M Y H:i:s') . ' GMT';
-header('Expires: ' . $now);
+header('Expires: 0'); // rfc2616 - Section 14.21
 header('Last-Modified: ' . $now);
 header('Cache-Control: no-store, no-cache, must-revalidate'); // HTTP/1.1
 header('Cache-Control: pre-check=0, post-check=0, max-age=0'); // HTTP/1.1