Make relative names in AXFR into FQDN

[niclan]

In the zonetransfer provider the RHS of a CNAME may be a relative name not necessarily a FQDN. So for example

www.example.com CNAME webserver

instead of

www.example.com CNAME webserver.example.com.

Note significant ending . in the second example. This PR makes relative names into FQDNs.