#1 Logging in different users from same IP

[Jeff Marshall]

When logging in as a different user from the same IP,
the user table in the database needs to wipe out the
last-known-IP for all other users on this same IP so
the logging goes to the latest known user at this IP.

Obviously, this is still avoiding the bigger issue of
when there are multiple active proxy users sitting
behind some firewall - they all appear as the same IP
address.