Move registration of CakePlugin.

Move the uses() call to Cake/bootstrap.php
CakePlugin is used by App, and should be loaded along with
other core classes like Configure and Cache.

Fixes #2147

lib/Cake/Core/App.php

@@ -739,7 +739,6 @@ class App {
 		self::$_map += (array)Cache::read('file_map', '_cake_core_');
 		self::$_objects += (array)Cache::read('object_map', '_cake_core_');
 		register_shutdown_function(array('App', 'shutdown'));
-		self::uses('CakePlugin', 'Core');
 	}
 
 /**

lib/Cake/bootstrap.php

@@ -130,6 +130,7 @@ spl_autoload_register(array('App', 'load'));
 
 App::uses('ErrorHandler', 'Error');
 App::uses('Configure', 'Core');
+App::uses('CakePlugin', 'Core');
 App::uses('Cache', 'Cache');
 App::uses('Object', 'Core');
 App::$bootstrapping = true;