This adds a slight patch to the HTTP analyzer, which recognizez when a connection is
upgraded to a different protocol (using a 101 reply with a few specific headers being
set).
In this case, the analyzer stops further processing of the connection (which will
result in DPD errors) and raises a new event:
event http_connection_upgrade(c: connection, protocol: string);
Protocol contains the name of the protocol that is being upgraded to, as specified in
one of the header values.
