/* ----------------------------------------------------------------------

  communicate atom coords and image flags in ireplica to all other replicas

  one proc per replica:

  if one proc per replica:

    direct overwrite via bcast

  else atoms could be stored in different order or on different procs:

    collect to root proc of event replica

  else atoms could be stored in different order on a proc or on different procs:

    gather to root proc of event replica

    bcast to roots of other replicas

    bcast within each replica

    each proc extracts info for atoms it owns using atom IDs