Fix issue2550954: History display breaks .. on removed properties: Now changes to removed properties, and link/unlink events from non-existing properties or classes no longer trigger a traceback. Concerning the visibility: We have a new config-item obsolete_history_roles in the main section that defines which roles may see removed properties. By default only role Admin is allowed to see these.

def audit_html_files(db, cl, nodeid, newvalues):
    if newvalues.has_key('type') and newvalues['type'] == 'text/html':
        newvalues['type'] = 'text/plain'
    

def init(db):
    db.file.audit('set', audit_html_files)
    db.file.audit('create', audit_html_files)