User Switching: avoid notice when placed in mu-plugins

gistfile1.diff

Index: trunk/user-switching.php
===================================================================
--- trunk/user-switching.php	(revision 416611)
+++ trunk/user-switching.php	(working copy)
@@ -19,12 +19,10 @@
 
 */
 
-if ( !defined( 'OLDUSER_COOKIE' ) )
-	define( 'OLDUSER_COOKIE', 'wordpress_olduser_' . COOKIEHASH );
-
 class user_switching {
 
 	function user_switching() {
+		add_action( 'plugins_loaded',   array( $this, 'set_old_cookie' ) );
 		add_action( 'admin_init',       array( $this, 'admin_init' ) );
 		add_action( 'admin_notices',    array( $this, 'admin_notice' ) );
 		add_action( 'user_row_actions', array( $this, 'user_row' ), 10, 2 );
@@ -34,6 +32,11 @@
 		add_action( 'wp_login',         'wp_clear_olduser_cookie' );
 	}
 
+	function set_old_cookie() {
+		if ( !defined( 'OLDUSER_COOKIE' ) )
+			define( 'OLDUSER_COOKIE', 'wordpress_olduser_' . COOKIEHASH );
+	}
+
 	function personal_options( $user ) {
 		$current_user = wp_get_current_user();
 		if ( !current_user_can( 'edit_user', $user->ID ) or ( $user->ID == $current_user->ID ) )