Handle whois referrals between RIRs

Handle whois referrals between RIRs

This is rather ugly, because the RIPE and APNIC whois servers do
not provide referrals for address blocks that they do not manage.
However ARIN is usually the right place or knows the right place
so we try there.

The particular instance which clued me in to this bug is U.Mich.
141.211.0.0/16 for which the referral chain should be IANA ->
RIPE -> ARIN. RIPE's RDAP does provide useful redirects (for
example try `curl -I http://rdap.db.ripe.net/ip/141.211.0.0)
so maybe their whois server can be improved.

AfriNIC's whois server gives more direct referrals, but they are
designed to be human-readable. Ugly, but we can manage.

The issue of referrals between RIRs is likely to become more important
in the future whith the increasing number of cross-region IP address
block transfers increases.