* Add vnode0,vnode1 slots to the delays table. This will allow us to
  match ipfw pipes to nodes after swapin, hopefully allowing us to
  control the delays for lans in addition to duplex links.

* Add IPaliases to interfaces table. Used in assign_wrapper when
  constructing "emulated" links, which will share a link via the use
  of aliases on the interface. This is a comma separated list of IP
  addresses (no, I refuse to make this a separate table!).

* Add virtnode_capacity slot to node_types, defaults to zero. This is
  used in ptopgen for determining how many virtnodes fit on a real
  node. I have not thought this through completely, but it allows me
  to make progress on other fronts.

* Add linkdelays delays, which sorta resembles the delays table, only
  this table stores oneway delays links, to be set up on the endpoints
  of a link or lan. Also, instead of being based on ipfw bridge rules,
  it is based on IP address/mask rules. At some point this table may
  merge witk the delays table, but will take time to work out the
  details and I do not want to mess up existing experiments by
  changing the delays table! Anyway, a duplex link gets one of these
  for each endpoint (a xmit ipfw rule). To mimic our lan setup, lan
  links get two, an xmit *and* a recv rule. My hope is that link
  delays will look just like normal delays (a packet leaving a node
  for a lan will get the outgoing delay, and a packet arriving gets
  the incoming delay).