/*
   * get child by index
   *
   * call-seq:
   *  node.get(42) -> XmlNode
   *  node.get(42, "name") -> XmlNode
   *  node.get(42, "name", "namespace") -> XmlNode
   *
   */
  WsXmlNodeH get(int i, const char *name = NULL, const char *ns = NULL) {