Index: wp-includes/plugin.php
===================================================================
--- wp-includes/plugin.php	(revision 24363)
+++ wp-includes/plugin.php	(working copy)
@@ -563,6 +563,7 @@
  * @uses WP_PLUGIN_DIR
  */
 function plugin_basename($file) {
+	$arg = $file;
 	$file = str_replace('\\','/',$file); // sanitize for Win32 installs
 	$file = preg_replace('|/+|','/', $file); // remove any duplicate slash
 	$plugin_dir = str_replace('\\','/',WP_PLUGIN_DIR); // sanitize for Win32 installs
@@ -571,7 +572,7 @@
 	$mu_plugin_dir = preg_replace('|/+|','/', $mu_plugin_dir); // remove any duplicate slash
 	$file = preg_replace('#^' . preg_quote($plugin_dir, '#') . '/|^' . preg_quote($mu_plugin_dir, '#') . '/#','',$file); // get relative path from plugins dir
 	$file = trim($file, '/');
-	return $file;
+	return apply_filters( 'plugin_basename', $file, $arg );
 }
 
 /**