rename user-id to loginname to stay consistent

lib/base.php

@@ -544,12 +544,12 @@ class OC {
 		OC_User::useBackend(new OC_User_Database());
 		OC_Group::useBackend(new OC_Group_Database());
 
-		if (isset($_SERVER['PHP_AUTH_USER']) && self::$session->exists('user_id')
+		if (isset($_SERVER['PHP_AUTH_USER']) && self::$session->exists('loginname')
 			&& $_SERVER['PHP_AUTH_USER'] !== self::$session->get('loginname')) {
 			$sessionUser = self::$session->get('loginname');
 			$serverUser = $_SERVER['PHP_AUTH_USER'];
 			OC_Log::write('core',
-				"Session user-id ($sessionUser) doesn't match SERVER[PHP_AUTH_USER] ($serverUser).",
+				"Session loginname ($sessionUser) doesn't match SERVER[PHP_AUTH_USER] ($serverUser).",
 				OC_Log::WARN);
 			OC_User::logout();
 		}