Core/AI: some tweaks on boundary functionality:

- Moved SetBoundary to public scope to allow for greater flexibility (ie set from external script)
- Extended to allow checking inverted boundaries

(cherry picked from commit 6892404b27)

src/server/scripts/Northrend/AzjolNerub/AzjolNerub/boss_anubarak.cpp

@@ -499,7 +499,7 @@ class npc_anubarak_anub_ar_assassin : public CreatureScript
                     Position jumpTo;
                     do
                         jumpTo = GetRandomPositionAround(anubarak);
-                    while (!CreatureAI::IsInBounds(boundary, &jumpTo));
+                    while (!CreatureAI::IsInBounds(*boundary, &jumpTo));
                     me->GetMotionMaster()->MoveJump(jumpTo, 40.0f, 40.0f);
                     DoCastSelf(SPELL_ASSASSIN_VISUAL, true);
                 }