security/zkt: Fix DragonFly regression

When this package was updated to version 1.1, it stopped building on
DragonFly.  The main issue is that DragonFly doesn't have bind in its
base.  NetBSD does, so it zkt finds it there, but otherwise it needs
the configuration switch --enable-binutil-path to be used.  This was
added for DragonFly to point at ${PREFIX}/sbin.

zkt requires bind to be installed in order to build.  Unlike other
packages like python, postgresql, and ruby where the mk.conf can
define a version otherwise a default is used, no such mechanism
exists to hand the four separate bind packages (at least I don't know
about one).  So the inclusion of bind99 is a hack I'm not too proud
of, but I don't have a better solution.  With it, it builds in clean
environments like pbulk chroot and Tinderbox.  If an individual user
is building from source, they'll be smart enough to comment out this
include if another version of bind is already installed (zkt will
fail on a bind build conflict).

I suspect DragonFly is rather unique in not having bind in base, so
for now this is left as a DragonFly-specific section.  Something
like net/bind99/builtin.mk could possibly be used to determine if
no builtin bind is available and thus follow DragonFly approach.  I
shall leave it to others to decide.


(marino)