AI: combat party
Actors with an AiFollow package should fight for the actor they are following.
(RM-1141 from redmine: created on 2014-01-28 by scrawl ., , closed on 2014-07-28 by scrawl ., relates #965 (closed), duplicates #1358 (closed), duplicates #1471 (closed), duplicates #1619 (closed))