reverted:
--- b/core/includes/bootstrap.inc
+++ a/core/includes/bootstrap.inc
@@ -2613,14 +2613,13 @@
     return $test_prefix;
   }
 
+  if (isset($_SERVER['HTTP_USER_AGENT']) && preg_match("/^(simpletest\d+);(.+);(.+);(.+)$/", $_SERVER['HTTP_USER_AGENT'], $matches)) {
-  $drupal_hash_salt = drupal_get_hash_salt();
-  if ($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
     // the database is not yet initialized and we can't access any Drupal variables.
     // The file properties add more entropy not easily accessible to others.
+    $key = drupal_get_hash_salt() . filectime(__FILE__) . fileinode(__FILE__);
-    $key = $drupal_hash_salt . filectime(__FILE__) . fileinode(__FILE__);
     $time_diff = REQUEST_TIME - $time;
     // Since we are making a local request a 5 second time window is allowed,
     // and the HMAC must match.