Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Import Magerya Vitaly's ldns-host, and build it instead of the BIND version
in the WITH_LDNS_UTILS case.

Approved by: re (blanket)

Import an LDNS-based implementation of host(1).