MDL-29008 lang: reintroduced error silencing to prevent unit test failures

lib/componentlib.class.php

@@ -326,7 +326,7 @@ class component_installer {
         @remove_dir($destinationcomponent.'_old');     // Deleting a possible old version.
 
         // Moving to a safe place.
-        $moveresult = rename($destinationcomponent, $destinationcomponent.'_old');
+        $moveresult = @rename($destinationcomponent, $destinationcomponent.'_old');
         if (!$moveresult) {
             debugging("Failed to rename {$destinationcomponent} to {$destinationcomponent}_old while installing a language");
         }