Initial implementation of IP address billing support:

Initial implementation of IP address billing support:

- bump versions of ahst/uhst/ghst/ghbh/asnt/usnt/gsnt to deal with new
  columns.

- Add correct offsets so access_host(), setup_ahst() and followup_ghst()
  deal with all versions of the queries.

- access_host():  Non query owner cannot create a host without a valid
  account number.

- Add setup_asnt() function, used by both asnt and usnt; don't allow
  creation of subnets whose "high" address is lower than the "low"
  address.