The next phase in the WINS rewrite!

The next phase in the WINS rewrite!

We now cope wiith multiple WINS groups and multiple failover servers
for release and refresh as well as registration. We also do the regitrations
in the same fashion as W2K does, where we don't try to register the next
IP in the list for a name until the WINS server has acked the previos IP.
This prevents us flooding the WINS server and also seems to make for much
more reliable multi-homed registration.

I also changed the dead WINS server code to mark pairs of IPs dead,
not individual IPs. The idea is that a WINS server might be dead from
the point of view of one of our interfaces, but not another, so we
need to keep talking to it on one while moving onto a failover WINS
server on the other interface. This copes much better with partial
LAN outages and weird routing tables.
(This used to be commit 313f2c9ff7a513802e4f893324865e70912d419e)