IP Address and Prefix Functions
  ===============================

    heavy lifting is done by the internal _normalize() function:

      _normalize(ip,normal,prefix[,part])  part := ['network','broadcast','netmask']

    here's the public interface with _normalize() args:

      ip address                prefix                     _normalize() args
      ------------------------  -------------------------  -------------------
      int    family(ipaddr)     int    family(prefix)       n/a

      ipaddr normalize(ipaddr)  prefix  normalize(prefix)  (ip,t,f/t)

      ipaddr host(ipaddr)       ipaddr host(prefix)        (ip,f,f)
      prefix text(ipaddr)       prefix text(prefix)        (ip,f,t)

                                prefix network(prefix)     (ip,f,t,'network')
                                ipaddr broadcast(prefix)   (ip,f,f,'broadcast')
                                ipaddr netmask(prefix)     (ip,f,f,'netmask')

                                int    masklen(prefix)     n/a
      ipaddr plus(ipaddr,int)                              n/a
      ------------------------  -------------------------  -------------------