If an unknown user from specified hosts quits in Excess flood,
with a 3-5 nick length, the bot will automatically put a ban.
New registry keys:
- protection.botnet.hosts: the hosts to ban, * allowed
- protection.botnet.banreason: the ban reason
- protection.botnet.banduration: the ban duration in minutes
New helper procedures in core:
- gethost: extracts the host part of a [nick!]user@host string
- isipv4, isipv6, isip: determines if a string is an ip
Fixes T515.