Add legacy wrapper

lib/legacy/cache.php

+<?php
+/**
+ * Copyright (c) 2013 Thomas Tanghus (thomas@tanghus.net)
+ * This file is licensed under the Affero General Public License version 3 or
+ * later.
+ * See the COPYING-README file.
+ */
+
+class Cache extends OC\Cache {
+}
\ No newline at end of file