fixing typo in redirection query string

Backport of a2cae551f3 to stable6

lib/private/util.php

@@ -580,7 +580,7 @@ class OC_Util {
 		// Check if we are a user
 		if( !OC_User::isLoggedIn()) {
 			header( 'Location: '.OC_Helper::linkToAbsolute( '', 'index.php',
-				array('redirectUrl' => OC_Request::requestUri())
+				array('redirect_url' => OC_Request::requestUri())
 			));
 			exit();
 		}