code: public void registerMailboxes(HostMessenger messenger) {
          for (Entry<OpsSelector, OpsAgent> entry : m_agents.entrySet()) {
              entry.getValue().registerMailbox(messenger,
                      entry.getKey().getHSId(messenger.getHostId()));
          }
      }
docs: Register the local mailboxes for each local OpsAgent.  Needs to be separated from
  construction so that any additional operations to make the OpsAgent ready for access
  can take place before requests get routed to it (example: registerStatsSource for StatsAgent)