rem: xmlDocPtr get_child ( xmlDocPtr node, gchar * child_name )
add: xmlNodePtr get_child ( xmlNodePtr node, gchar * child_name )
context: xmlDocPtr get_child ( xmlDocPtr node, gchar * child_name ){  xmlDocPtr iter_node = node -> children;  if (!node) return NULL;  while ( iter_node )    {      if ( node_strcmp(iter_node, child_name) )	return iter_node;      iter_node = iter_node -> next;    }  return NULL;}