I've been using
http://www-old.bro-ids.org/wiki/index.php/Reference_Manual lately. It
appears to be a better reference for learning how to write Bro scripts
than http://www.bro-ids.org/documentation/index.html . Is
http://www-old.bro-ids.org/wiki/index.php/Reference_Manual still the
recommended place to learn the Bro scripting language?


Unfortunately if you are learning the language in deeper detail that is probably the best documentation around right now. The only thing to keep in mind is that the newer script structure and new idioms to script development aren't documented there. Once we have better documentation we may likely retire that old site permanently.