Index: wp-admin/admin-ajax.php
===================================================================
--- wp-admin/admin-ajax.php	(revision 21064)
+++ wp-admin/admin-ajax.php	(working copy)
@@ -38,7 +38,7 @@
 
 $core_actions_get = array(
 	'fetch-list', 'ajax-tag-search', 'wp-compression-test', 'imgedit-preview', 'oembed-cache',
-	'autocomplete-user', 'dashboard-widgets',
+	'autocomplete-user', 'dashboard-widgets', 'logged-in',
 );
 
 $core_actions_post = array(
Index: wp-admin/includes/ajax-actions.php
===================================================================
--- wp-admin/includes/ajax-actions.php	(revision 21064)
+++ wp-admin/includes/ajax-actions.php	(working copy)
@@ -212,6 +212,10 @@
 	wp_die();
 }
 
+function wp_ajax_logged_in() {
+	wp_die( 1 );
+}
+
 /*
  * Ajax helper.
  */