House owners can add 'friends' to the friends list of the
house. All characters on the account of the house owner will
be auto-friended to the house, except characters that are
owners of another house.
All players who are not on the friends list of a player
building will highlight grey to the owner and his friends
if they enter that building. This allows the owner and friends
to deal with trespassers without fear of getting flagged.