message: Add error if trying to read on a reduced number of processors.
diff: @@ -723,6 +723,8 @@ void IOManager::readSidreHDF5(sidre::Group* datagroup,
  int num_files = getNumFilesFromRoot(root_file);
  int num_groups = getNumGroupsFromRoot(root_file);
  SLIC_ASSERT(num_files > 0);
  + SLIC_ERROR_IF(num_groups > m_comm_size,
  + "IOManager cannot read from files written by more ranks than are being used in the current run.");
  if (m_baton)
  {
  