Index: wp-includes/wp-diff.php
===================================================================
--- wp-includes/wp-diff.php	(revision 8579)
+++ wp-includes/wp-diff.php	(working copy)
@@ -1,9 +1,9 @@
 <?php
 
 if ( !class_exists( 'Text_Diff' ) ) {
-	require( 'Text/Diff.php' );
-	require( 'Text/Diff/Renderer.php' );
-	require( 'Text/Diff/Renderer/inline.php' );
+	require( dirname(__FILE__).'/Text/Diff.php' );
+	require( dirname(__FILE__).'/Text/Diff/Renderer.php' );
+	require( dirname(__FILE__).'/Text/Diff/Renderer/inline.php' );
 }
 
 
Index: wp-includes/Text/Diff/Renderer/inline.php
===================================================================
--- wp-includes/Text/Diff/Renderer/inline.php	(revision 8579)
+++ wp-includes/Text/Diff/Renderer/inline.php	(working copy)
@@ -14,8 +14,10 @@
  */
 
 /** Text_Diff_Renderer */
-require_once 'Text/Diff/Renderer.php';
 
+// WP #7391
+require_once dirname(__FILE__).'/../Renderer.php';
+
 /**
  * "Inline" diff renderer.
  *
Index: wp-includes/Text/Diff.php
===================================================================
--- wp-includes/Text/Diff.php	(revision 8579)
+++ wp-includes/Text/Diff.php	(working copy)
@@ -49,7 +49,8 @@
             $engine = basename($engine);
         }
 
-        require_once 'Text/Diff/Engine/' . $engine . '.php';
+        // WP #7391
+        require_once dirname(__FILE__).'/Diff/Engine/' . $engine . '.php';
         $class = 'Text_Diff_Engine_' . $engine;
         $diff_engine = new $class();
 
Index: wp-includes/pluggable.php
===================================================================
--- wp-includes/pluggable.php	(revision 8579)
+++ wp-includes/pluggable.php	(working copy)
@@ -1530,10 +1530,6 @@
 	$defaults = array( 'title' => '', 'title_left' => '', 'title_right' => '' );
 	$args = wp_parse_args( $args, $defaults );
 
-	// PEAR Text_Diff is lame; it includes things from include_path rather than it's own path.
-	// Not sure of the ramifications of disttributing modified code.
-	ini_set('include_path', '.' . PATH_SEPARATOR . ABSPATH . WPINC );
-
 	if ( !class_exists( 'WP_Text_Diff_Renderer_Table' ) )
 		require( ABSPATH . WPINC . '/wp-diff.php' );
 
@@ -1552,8 +1548,6 @@
 	$renderer  = new WP_Text_Diff_Renderer_Table();
 	$diff = $renderer->render($text_diff);
 
-	ini_restore('include_path');
-
 	if ( !$diff )
 		return '';