DHCP in v2.2

[Alan DeKok]

  Arran and I have made a number of tests with the current DHCP code.
They exposed some minor issues, mostly unclear debug output.  Those have
been fixed, and we're in the process of syncing v2.2.x and master.

  The DHCP code works with everything we can throw at it.  So I think
it's good to go.

  Arran is also working on higher performance IP Pools in SQL.  That
should mean people running custom ISC configs can finally move to using
a real database.

  Alan DeKok.