Faster client lookups

I've hacked the "client lookup" code so that it's now looking up clients in binary trees. This should allow 10^6 or so clients/server without the current linear lookup. I've updated the SQL "read clients" code, but I don't have SQL, so I haven't checked if it works. The change also removes the "get list of clients" from SNMP feature, but I don't see that as all that critical. Alan DeKok.