pkgin autoremove equivalent

[Jason Bacon <jtocino%gmx.com@localhost>]

Is there a simple equivalent to pkgin autoremove using just pkg_install
commands?  I could use pkg_info -Ba to identify automatically installed
packages along with a clunky script to parse the output.

Could also install pkgin just for this purpose, but much of its
functionality won't work without a binary package repo available, so
it's a bit kludgy and occasionally disruptive having it present in an
installation where everything is built from source.

Thanks,

	JB