FileAnalysis: add unit tests covering current protocol integration.

And had to make various fixes/refinements after scrutinizing results.

scripts/base/protocols/irc/file-analysis.bro

@@ -5,6 +5,7 @@
 redef FileAnalysis::service_handle_callbacks += {
 	["irc-dcc-data"] = function(c: connection, is_orig: bool): string
 		{
+		if ( is_orig ) return "";
 		return fmt("%s irc-dcc-data: %s", c$start_time, id_string(c$id));
 		},
 };