reverted:
--- b/core/lib/Drupal/Core/Annotation/DirectoryIterator.php
+++ /dev/null
@@ -1,27 +0,0 @@
-<?php
-
-/**
- * @file
- * Definition of Drupal\Core\Annotation\DirectoryIterator.
- */
-
-namespace Drupal\Core\Annotation;
-
-use DirectoryIterator as PHPDirectoryIterator;
-
-/**
- * This class exists to support pre-5.3.6 versions of php where this method
- * does not exist. Once the requirements for core are upgraded, this class can
- * be removed.
- */
-class DirectoryIterator extends PHPDirectoryIterator {
-
-  /**
-   * @todo.
-   */
-  public function getExtension() {
-    $parts = explode('.', $this->getFilename());
-    return array_pop($parts);
-  }
-
-}
diff -u b/core/lib/Drupal/Core/Plugin/Discovery/AnnotatedClassDiscovery.php b/core/lib/Drupal/Core/Plugin/Discovery/AnnotatedClassDiscovery.php
--- b/core/lib/Drupal/Core/Plugin/Discovery/AnnotatedClassDiscovery.php
+++ b/core/lib/Drupal/Core/Plugin/Discovery/AnnotatedClassDiscovery.php
@@ -7,9 +7,9 @@
 
 namespace Drupal\Core\Plugin\Discovery;
 
+use DirectoryIterator;
 use Drupal\Component\Plugin\Discovery\DiscoveryInterface;
 use Drupal\Component\Reflection\MockFileFinder;
-use Drupal\Core\Annotation\DirectoryIterator;
 use Drupal\Core\Annotation\Plugin;
 use Doctrine\Common\Annotations\AnnotationReader;
 use Doctrine\Common\Annotations\AnnotationRegistry;
@@ -57,7 +57,9 @@
         if (file_exists($dir)) {
           $directories = new DirectoryIterator($dir);
           foreach ($directories as $fileinfo) {
-            if ($fileinfo->getExtension() == 'php') {
+            // @TODO: Once core requires 5.3.6 use $fileiinfo->getExtension()
+            // instead.
+            if (pathinfo($fileinfo->getFilename(), PATHINFO_EXTENSION) == 'php') {
               $class = str_replace(DIRECTORY_SEPARATOR, '\\', "$prefix/". $fileinfo->getBasename('.php'));
               // The file name is already known so no need to find the file,
               // but StaticReflectionParser needs one so use a mock version.
diff -u b/core/modules/aggregator/lib/Drupal/aggregator/Plugin/FetcherManager.php b/core/modules/aggregator/lib/Drupal/aggregator/Plugin/FetcherManager.php
--- b/core/modules/aggregator/lib/Drupal/aggregator/Plugin/FetcherManager.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/Plugin/FetcherManager.php
@@ -8,8 +8,9 @@
 namespace Drupal\aggregator\Plugin;
 
 use Drupal\Component\Plugin\PluginManagerBase;
-use Drupal\Core\Plugin\Discovery\AnnotatedClassDiscovery;
 use Drupal\Component\Plugin\Factory\DefaultFactory;
+use Drupal\Core\Plugin\Discovery\AnnotatedClassDiscovery;
+use Drupal\Core\Plugin\Discovery\CacheDecorator;
 
 /**
  * Manages aggregator fetcher plugins.
@@ -17,7 +18,7 @@
 class FetcherManager extends PluginManagerBase {
 
   public function __construct() {
-    $this->discovery = new AnnotatedClassDiscovery('aggregator', 'fetcher');
+    $this->discovery = new CacheDecorator(new AnnotatedClassDiscovery('aggregator', 'fetcher'), 'aggregator:fetcher', 'plugin');
     $this->factory = new DefaultFactory($this->discovery);
   }
 }
only in patch2:
unchanged:
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -3367,7 +3367,7 @@ function system_cron() {
     }
   }
 
-  $cache_bins = array_merge(module_invoke_all('cache_flush'), array('form', 'menu'));
+  $cache_bins = array_merge(module_invoke_all('cache_flush'), array('form', 'menu', 'plugin'));
   foreach ($cache_bins as $bin) {
     cache($bin)->expire();
   }