Pass false as the 2nd argument to class_exists() to disable autoloading and to not cause problems for those who define __autoload().

Fixes #20523.

Built from https://develop.svn.wordpress.org/trunk@34348


git-svn-id: http://core.svn.wordpress.org/trunk@34312 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/class-feed.php

@@ -1,6 +1,6 @@
 <?php
 
-if ( !class_exists('SimplePie') )
+if ( ! class_exists( 'SimplePie', false ) )
 	require_once( ABSPATH . WPINC . '/class-simplepie.php' );
 
 class WP_Feed_Cache extends SimplePie_Cache {