mod_adhoc_dataforms_demo: Fix duplicate field prevention It's supposed to only include each type of form field once per form at most but it didn't note which fields it had added already. No idea what the probability was anyways, probably pretty low.

module:hook("authentication-success", function (event)
	local session = event.session;
	local sasl_handler = session.sasl_handler;
	session.log("info", "Authenticated with %s", sasl_handler and sasl_handler.selected or "legacy auth");
end);