Support FreeBSD 10.0.
On FreeBSD 10.0, all configuration is installed under
/usr/local/etc/namedb and installs its own rc script in
$PREFIX, which no longer support chroot installations.
LINKS and REPLACE_BASE options are not supported on 10.0
for obvious reasons.
Note for FreeBSD 9.x and earlier users, LINKS is no longer
the default option, though still supported.
An UPDATING entry will follow after bind99 is fixed