[WIP] substitute pkgng for pkg_info

"pkgng" is the new package manager.
  see http://www.freebsd.org/doc/en/books/handbook/pkgng-intro.html

I suppose it should use pkgng instead of pkg_info, pkg_add, and such.
pkgng supports FreeBSD 9.1 over, and moreover, pkg_info and such have
been removed since FreeBSD 10.0-CURRENT.