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.