s4:provision - Bump down the domain and forest level to Windows 2000

s4:provision - Bump down the domain and forest level to Windows 2000

- The DC level we keep on Windows Server 2008 R2 (we should call ourself
  always the newest server type)
- The domain/forest level we set to the minimum (Windows 2000 native) to
  allow all AD DC types (from Windows 2000 on) in our domain - the NT4 "mixed"
  mode isn't supported by us (discussed on mailing list) -> "nTMixedDomain" is
  set always to 0
- I'll add a script which allows to bump the DC level (basically sets the
  "msDS-Behaviour-Version" attributes on the "Partitions/Configuration/DC" and
  on the "DC" object)