Adding import for String to ensure that String has been loaded when S…

…ecurity component is used without making any database connections. Fixes #482

cake/libs/controller/components/security.php

@@ -23,6 +23,7 @@
  * @lastmodified  $Date$
  * @license       http://www.opensource.org/licenses/mit-license.php The MIT License
  */
+App::import('Core', 'String');
 /**
  * Short description for file.
  *