Handle timeout exception in roundup-server better. A timeout in roundup-server used to generate another exception: OSError: cannot read from timed out object when it tried to reuse the socket that timed out. Now return status 408, a brief message and trigger closing of the socket. Manual testing, no CI. To test used curl -X POST with no --data defined.

def audit_html_files(db, cl, nodeid, newvalues):
    if 'type' in newvalues 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)