Add unzip(1). If you can't beat 'em, join 'em

Add unzip(1). If you can't beat 'em, join 'em

The unzip utility isn't particularly necessary (the version of unzip in
ports is better), but the ports tree does leverage it extensively.  I've
been patching around all the resulting failures, but it's easier just to
import unzip(1) from FreeBSD and remove the ports tree modifications.

This tool has also been available in NetBSD since version 6.0, so maybe
bringing it into DragonFly will establish it as a standard BSD utility.