Fix generation of IXP related addresses.  ixpN now resolves to the IXP itself rather than the pc hosting the IXP.
Fix generation of IXP related addresses.  ixpN now resolves to the IXP itself
rather than the pc hosting the IXP.

Also add option to generated forward file with hosts sorted by IP
(not turned on).

nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome