message: Change default "tree_pattern" in SPIO index
diff: @@ -93,7 +93,7 @@ public:
  int num_files,
  const std::string& file_string,
  const std::string& protocol,
  - const std::string& tree_pattern = "datagroup_%07d");
  + const std::string& tree_pattern = "datagroup");
  /*!
  * \brief write additional group to existing root file
  