only in patch2:
unchanged:
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -2601,7 +2601,7 @@ function drupal_valid_test_ua($new_prefix = NULL) {
     return $test_prefix;
   }
 
-  if (isset($_SERVER['HTTP_USER_AGENT']) && preg_match("/^(simpletest\d+);(.+);(.+);(.+)$/", $_SERVER['HTTP_USER_AGENT'], $matches)) {
+  if ($drupal_hash_salt && isset($_SERVER['HTTP_USER_AGENT']) && preg_match("/^(simpletest\d+);(.+);(.+);(.+)$/", $_SERVER['HTTP_USER_AGENT'], $matches)) {
     list(, $prefix, $time, $salt, $hmac) = $matches;
     $check_string =  $prefix . ';' . $time . ';' . $salt;
     // We use the salt from settings.php to make the HMAC key, since