inotify-based fileserver-backend index updater
as the fileserver backend is read-only, new content gets there by non-wiki means (e.g. via direct access to the filesystem) and backend storage contents changes behind moin's back.
moin's index is currently only updated on a indexing run (or when contents are changed via moin, which is not the case here), so the index data is not automatically updated when the fs changes.
we could watch the fs with inotify (see pyinotify) and update the index when we get a change notification.