Add means to restrict auto_ptr to existing zones

[dmgeurts]

Feature request

Please could a setting be added for not adding a new reverse (arpa) zone, when auto_ptr is enabled? I've added the arpa zones that we're responsible for as per RIPE, but have clients with IP addresses not owned by us. I'd like to avoid having to regularly remove reverse zones not owned by us.

Thanks, for a great piece of software. I wish I had the time and know-how to add the code myself.