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/kalimdor/temple_of_ahnqiraj/boss_twinemperors.cpp

@@ -258,12 +258,11 @@ struct boss_twinemperorsAI : public ScriptedAI
             {
                 AfterTeleport = false;
                 me->clearUnitState(UNIT_STAT_STUNNED);
-                Unit *nearu = me->SelectNearestTarget(100);
-                //DoYell(nearu->GetName(), LANG_UNIVERSAL, 0);
-                if (nearu)
+                if (Unit *nearu = me->SelectNearestTarget(100))
                 {
+                    //DoYell(nearu->GetName(), LANG_UNIVERSAL, 0);
                     AttackStart(nearu);
-                    me->getThreatManager().addThreat(nearu, 10000);
+                    me->AddThreat(nearu, 10000);
                 }
                 return true;
             }