Import unblock-lan-zones feature backported from upstream svn trunk.
This is a partial fix for reverse lookups in RFC 1918 networks. With
this option enabled, unbound no longer ignores these queries; however,
it will still reject the answer it gets from the forwarder, because
the RFC 1918 reverse zones are signed.

Submitted by: "W.C.A. Wijngaards" <wouter@nlnetlabs.nl>