Core/Auras: Add some asserions to hunt down reason of a crash in Aura::UpdateTargetMap. Thanks to Shauren for inspiration.

--HG--
branch : trunk

src/server/game/Entities/Unit/Unit.cpp

@@ -3468,6 +3468,9 @@ AuraApplication * Unit::_CreateAuraApplication(Aura * aura, uint8 effMask)
     // aura musn't be removed
     ASSERT(!aura->IsRemoved());
 
+    // aura mustn't be already applied on target
+    ASSERT (!aura->IsAppliedOnTarget(GetGUID()) && "Unit::_CreateAuraApplication: aura musn't be applied on target");
+
     SpellEntry const* aurSpellInfo = aura->GetSpellProto();
     uint32 aurId = aurSpellInfo->Id;