issue2550749 - the xmlrpc interface is invoked on content type and not url path. Sending any text/xml data to roundup results in invoking the xml-rpc interface, but a REST or other interface could also consume xml data and do something different. So require the use of 'http(s)://.../xmlrpc' uri to trigger the xmlrpc interface.

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)