now via the RFC 2369 `list_id` instead of the fqdn listname (i.e. posting
  address).  This is because while the posting address can change if the
  mailing list is moved to a new server, the list id is fixed.
  (LP: #1024509)
  + IListManager.get_by_list_id() added.
  + IListManager.list_ids added.
  + IMailingList.list_id added.
  + Several internal APIs that accepted fqdn list names now require list ids,
    e.g. ISubscriptionService.join() and .find_members().
  + IMember.list_id attribute added; .mailing_list is now an alias that
    retrieves and returns the IMailingList.
  - list_id added (LP: #1024509)