It relies on the heuristics of GridFTP data channels commonly default to
SSL mutual authentication with a NULL bulk cipher and that they usually
transfer large datasets (default threshold of script is 1 GB). The
script also defaults to skip_further_processing() after detection to try
to save cycles analyzing the large, benign connection.
Also added a script in base/protocols/conn/polling that generalizes the
process of polling a connection for interesting features. The GridFTP
data channel detection script depends on it to monitor bytes
transferred.
