Core/Spells: Store explicit unit, corpse and GO targets in one variable, because both client and server can't handle more than one explicit object target; Add spell explicit target validation.

src/server/game/Entities/Object/Object.h

@@ -328,6 +328,9 @@ class Object
         const Unit* ToUnit() const {if (GetTypeId() == TYPEID_UNIT || GetTypeId() == TYPEID_PLAYER) return (const Unit*)((Unit*)this); else return NULL; }
         GameObject* ToGameObject(){ if (GetTypeId() == TYPEID_GAMEOBJECT) return reinterpret_cast<GameObject*>(this); else return NULL; }
         const GameObject* ToGameObject() const {if (GetTypeId() == TYPEID_GAMEOBJECT) return (const GameObject*)((GameObject*)this); else return NULL; }
+
+        Corpse* ToCorpse(){ if (GetTypeId() == TYPEID_CORPSE) return reinterpret_cast<Corpse*>(this); else return NULL; }
+        const Corpse* ToCorpse() const {if (GetTypeId() == TYPEID_CORPSE) return (const Corpse*)((Corpse*)this); else return NULL; }
     protected:
 
         Object ();