(plaintiff sued defendant seeking declaratory judgment that defendant obligated to defend plaintiff against claims of other property owners; plaintiff’s property bordered lake Michigan and question arose concerning boundary and others using beach and crossing and occupying what plaintiff believed to be plaintiff’s property; policy exceptions excluded from coverage “boundary line disputes not disclosed of record” and rights of “adjacent and abutting property owners in that portion of the premises lying along Grand Traverse Bay”; court holds that duty-to-defend coverage in general terms of policy not negated by exceptions; boundary line dispute was disclosed of record).