Water creatures attempt to attack players who don't enter the water

For example, walk on the docks in Hla Olad. Battle music begins to play, triggered presumably by the lone slaughterfish that hangs around there.

(RM-2767 from redmine: created on 2015-07-10 by Nicola Bodill, , closed on 2016-12-11 by nobody, relates #2172 (closed), relates #2678 (closed))