MFH (r292206): upgrade to Unbound 1.5.7
MFH (r292135): run configure script with correct compiler

MFH (r287917, r287918, r289063): upgrade to latest Unbound
MFH (r283301, r289592, r291582): rc script improvements
MFH (r287880): respect manually configured forwarders when using DHCP
MFH (r289321): deconfuse man page

PR: 184047 203580 204931

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

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

Minimal subset of the unbound sources.

import unbound 1.4.17