Feature: Disable forwading on per-zone basics
Reason: Some setups require to disable forwading per-zone. For example company servers are configured as authoritative for non-public zone and have global forwarding turned on. When the non-public zone contains delegation for non-public subdomain, the zone must have explicitly disable forwarding otherwise the glue won't be returned.
Result (if any): Server can return delegation glue for private zones when global forwarding is turned on.