- Failover rebalance events no longer play ping pong with round errors

- Failover rebalance events no longer play ping pong with round errors
  (moving leases between free and back to backup where there are an
  odd number of leases).
  [ISC-Bugs #16910]

- The 'pool' log line has been split into two messages, one before the
  rebalance run, and one after.
  [ISC-Bugs #16910]

- Any queued BNDACKs are transmitted before transmitting new BNDUPDs.
  This enforces the correct sequence of events for the remote server
  processing these messages.
  [ISC-Bugs #16910]