Add get_reverse_domain_name functionality
Add get_reverse_domain_name functionality

In this way the reverse it is possible to create
auto-ptr records in higher ip classes (eg. class A in IPv4).
Only works with existing higher class domain.

If is isn't find higher class domain, create a lowest class domain, and add there the reverse PTRs.

Also works with IPv6!
ivanfilippov/PowerDNS-Admin,ivanfilippov/PowerDNS-Admin,ivanfilippov/PowerDNS-Admin,0x97/PowerDNS-Admin,0x97/PowerDNS-Admin,0x97/PowerDNS-Admin,0x97/PowerDNS-Admin,ivanfilippov/PowerDNS-Admin