Use AnyEvent::HTTP in the checker

Mirror::Trace no longer fetches the trace file itself, which was a
silly thing to do. Threads are no longer used.
Allow some more input data when processing a non-200 response

Many 404s are aborted and not reported as such otherwise.
Use AnyEvent in the update.pl script

Gets rid off the ridiculous use of threads with synchronous DNS
queries.
Ensure that 'ipv6: yes' mirrors do have a AAAA rr

First stone for issue #15 and other IPv6 stuff
Don't call update.pl with -j, it is now useless
Split the db into an ipv4 and ipv6 subtrees

For compatibility add all the existing, top-level, structures as
references to the ipv4 subtree.
Split the processing of mirrors based on IP family

Closes #11 as it is now possible to have IPv6-only mirrors - at least
as far as the database is concerned.
Include the ip family when printing the hostname
Add support for different IP families

The IP family to be checked needs to be specified via --ipv
Add support for the ipv6 db to translate-log
Drop --store-traces, they are already stored in the db
debian-ports support: update demo page and doc

To complete 1c3689271
Allow different IP families to be checked on the same run

They are run sequentially, but that's due to a limitation in AnyEvent
Store the db at the end of every ip family check

This is still not ideal, but reduces the time it takes to finally
populate the results.
Merge branch 'anyevent/check6'