Improve docs and add reset() method.

Add a reset() method, while I don't think it will be widely useful it
could be helpful in testing situations and is simple to support and
maintain.

lib/Cake/Test/TestCase/Controller/ComponentRegistryTest.php

@@ -165,4 +165,20 @@ public function testGetController() {
 		$result = $this->Components->getController();
 		$this->assertInstanceOf('Cake\Controller\Controller', $result);
 	}
+
+/**
+ * Test reset.
+ *
+ * @return void
+ */
+	public function testReset() {
+		$instance = $this->Components->load('Paginator');
+		$this->assertSame(
+			$instance,
+			$this->Components->Paginator,
+			'Instance in registry should be the same as previously loaded'
+		);
+		$this->assertNull($this->Components->reset(), 'No return expected');
+		$this->assertNotSame($instance, $this->Components->load('Paginator'));
+	}
 }

lib/Cake/Utility/ObjectRegistry.php

@@ -19,8 +19,9 @@
  * Provides registry & factory functionality for object types. Used
  * as a super class for various composition based re-use features in CakePHP.
  *
- * Each subclass needs to implement its own load() functionality. Replaces ObjectCollection
- * in previous versions of CakePHP.
+ * Each subclass needs to implement the various abstract methods to complete
+ * the template method load(). This class replaces ObjectCollection
+ * from previous versions of CakePHP.
  *
  * @since CakePHP 3.0
  * @see Cake\Controller\ComponentRegistry
@@ -40,10 +41,12 @@ abstract class ObjectRegistry {
  * Loads/constructs a object instance.
  *
  * Will return the instance in the registry if it already exists.
- * You can use `$settings['enabled'] = false` to disable events on an object when loading it.
- * Not all registry subclasses support events.
+ * If a subclass provides event support, you can use `$settings['enabled'] = false`
+ * to exclude constructed objects from being registered for events.
+ *
+ * Using Cake\Controller\Controller::$components as an example. You can alias 
+ * an object by setting the 'className' key, i.e.,
  *
- * You can alias an object by setting the 'className' key, i.e.,
  * {{{
  * public $components = [
  *   'Email' => [
@@ -163,4 +166,13 @@ public function normalizeArray($objects) {
 		return $normal;
 	}
 
+/**
+ * Clear loaded instances in the registry.
+ *
+ * @return void
+ */
+	public function reset() {
+		$this->_loaded = [];
+	}
+
 }