serialization support for shared_ptr, unique_ptr objects

[jjwilke]

Code needed for serialize_serializable:

template <class T>
class serialize<std::shared_ptr<T> > {
 public:
  void operator()(std::shared_ptr<T>& o, serializer& ser){
    T* tmp = o.get();
    serialize_intrusive_ptr(tmp, ser);
    o = std::shared_ptr<T>(tmp);
  }
};

Also, should probably change name of serialize_intrusive_ptr to serialize_serializable_ptr