Index: wp-includes/rewrite.php
===================================================================
--- wp-includes/rewrite.php	(revision 16500)
+++ wp-includes/rewrite.php	(working copy)
@@ -1881,6 +1881,7 @@
 	function flush_rules($hard = true) {
 		delete_option('rewrite_rules');
 		$this->wp_rewrite_rules();
+                $hard = apply_filters('flush_rewrite_rules_hard', $hard);
 		if ( $hard && function_exists('save_mod_rewrite_rules') )
 			save_mod_rewrite_rules();
 		if ( $hard && function_exists('iis7_save_url_rewrite_rules') )