Wicket file storage bloating

DiskPageStore doesn't cleanup old/invalid session data. AFAIK there are two scenarios when it forgets about content in wicket file store folder:

• normal restart of tomcat, index was saved, however all sessions that were invalidated by restart - files for them will never be cleaned up.
• tomcat went down, index file was not saved - whole wicket file store now contains files that will never be cleaned up.