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 init_severity(db, cl, nodeid, newvalues):
    """Make sure severity is set on new issues"""
    if newvalues.has_key('severity') and newvalues['severity']:
        return

    normal = db.severity.lookup('normal')
    newvalues['severity'] = normal

def init(db):
    db.issue.audit('create', init_severity)