message: Reduce PrintNodes output when instancing.
  Only fully print the main node.  All others printed as instances only.
diff: @@ -35,9 +35,7 @@ namespace ospray::sg {
  inline bool PrintNodes::operator()(Node &node, TraversalContext &ctx)
  {
  - for (int i = 0; i < ctx.level; i++)
  - std::cout << " ";
  - std::cout << node.name() << " : " << node.subType();
  + std::cout << std::string(2*ctx.level, ' ') << node.name() << " : " << node.subType();
  // A couple of usings to make subType strings match types
  using string = std::string;
  @@ -61,6 +59,12 @@ namespace ospray::sg {
  PRINT_AS(node, Transform);
  std::cout << std::endl;
  + // XXX Debug only, probably need something better here.
  + // Don't litter the PrintNodes with copies of instances, only fully traverse
  + // the main one hanging off world.
  + if (ctx.level > 2 && node.subType().find("importer_") != std::string::npos)
  + return false;
  +
  return true;
  }
  