Features/forward zones

This simple fix allows creating of forward-zones. I also included line in readme where this can be useful. 
However for some problems:
If auto-trust-anchor-file enabled, resolving of external names will fail due to DNSSEC(?) with:
2013-04-18T16:14:34.924873+04:00 primary-dns unbound: [1753:0] info: failed to prime trust anchor -- DNSKEY rrset is not secure . DNSKEY IN
I'm still investigating, but maybe you already know what's wrong :)