Remove reject entries on unkline/ungline/unxline.

Remove reject entries on unkline/ungline/unxline.
When a user is rejected, remember the hash value of the
ban mask (for klines/glines, hash value of the user part
XOR hash value of the host part) with the rejected IP;
if the kline/gline/xline is removed, remove rejects with
the same hash value also.  Note that this does not happen
for expiries; this is deliberate.
Rejects for no auth{} or dnsbl put a hash value of 0;
they cannot be removed selectively.