message: optimize away the need to create a temporary shared_ptr for Handle::operator->()
diff: @@ -92,7 +92,7 @@ namespace ospray {
  Handle operator+= (Handle n)
  { get()->add(n); n->setParent(*this); return n;}
  - std::shared_ptr<sg::Node> operator->() const { return get(); }
  + sg::Node* operator->() const { return node.get(); }
  std::shared_ptr<sg::Node> get() const { return node; }
  