Don't block IP's if they are listed in xbl.spamhaus.org.

xbl.spamhaus.org is intended for use only on incoming mail, it contains
mostly dynamic IP addresses.
Using it for anything other than it's intended purpose may block
legitimate users.
Merge branch 'master' of https://github.com/jd4564/Pokemon-Showdown into update
Improve DNSBL support.
Improve DNSBL support.
Merge branch 'update' of https://github.com/jd4564/Pokemon-Showdown into update