encode German Eszett for afnic tlds

according to this document:
http://www.afnic.fr/medias/documents/afnic-idn-technical-specifications.pdf
(section 1.5)

afnic uses the same rules as denic for encoding Eszett characters.
so i have added the afnic tlds to the _punycode_segments zone check
and also added a couple of tests for these cases
raised version for release
Merge pull request #4 from studo/afnic-idn

Afnic idn