Refactor Creature::SelectNearestTarget(float dist)

This function is used in many scripts to find the nearest enemy within the given distance.
However, it had an implicit limit to the ATTACK_DISTANCE. so in many case the "dist" was in fact just ignored.
In other case, the ATTACK_DISTANCE is required. So 2 functions are necessary to avoid ambiguities.

The refactoring is the split of the function in 2: SelectNearestTarget and SelectNearestTargetInAttackDistance.

--HG--
branch : trunk

src/scripts/northrend/naxxramas/boss_four_horsemen.cpp

@@ -236,6 +236,16 @@ struct boss_four_horsemenAI : public BossAI
         nextWP = id + 1;
     }
 
+    // switch to "who" if nearer than current target.
+    void SelectNearestTarget(Unit *who)
+    {
+        if (me->getVictim() && me->GetDistanceOrder(who, me->getVictim()) && me->canAttack(who))
+        {
+            me->getThreatManager().modifyThreatPercent(me->getVictim(), -100);
+            me->AddThreat(who, 1000000.0f);
+        }
+    }
+
     void MoveInLineOfSight(Unit *who)
     {
         BossAI::MoveInLineOfSight(who);