/**
* @see FileBackend::__construct()
* Additional $config params include:
- * - srvCache : BagOStuff cache to APC/XCache or the like.
+ * - srvCache : BagOStuff cache to APC or the like.
* - wanCache : WANObjectCache object to use for persistent caching.
* - mimeCallback : Callback that takes (storage path, content, file system path) and
* returns the MIME type of the file or 'unknown/unknown'. The file