In detail:

1. Added TBDB_NODESTATE_ALWAYSUP to libdb.pm for representing the ALWAYSUP
eventstate.

2. Modified free node calculation in ptopgen to include ALWAYSUP nodes.

3. Added code to ptopgen to correctly handle the case of a NULL iface
column, which happens when switches have interface (as they do in
Wisconsin), but assign_wrapper expects (null) for their iface rather than
"".