message: Fix upgrade path for legacy documents
  This changelist fixes a bug in the upgrade path for constant nodes in v1.25 documents.
diff: @@ -388,15 +388,12 @@ void Document::upgradeVersion()
  {
  for (ElementPtr elem : traverseTree())
  {
  - if (elem->isA<Node>("constant"))
  + if (elem->getCategory() == "constant")
  {
  - NodePtr constant = elem->asA<Node>();
  - ParameterPtr colorParam = constant->getChildOfType<Parameter>("color");
  - if (colorParam)
  + ElementPtr param = elem->getChild("color");
  + if (param)
  {
  - ParameterPtr valueParam = constant->addParameter("value");
  - valueParam->copyContentFrom(colorParam);
  - constant->removeParameter(colorParam->getName());
  + param->setName("value");
  }
  }
  }
  