Adding missing import that causes a fatal error when a deep

value is written to Configure early on.
Fixes #1753

lib/Cake/Core/Configure.php

@@ -17,6 +17,8 @@
  * @license       MIT License (http://www.opensource.org/licenses/mit-license.php)
  */
 
+App::uses('Set', 'Utility');
+
 /**
  * Configuration class. Used for managing runtime configuration information.
  *