Added unpublish method and tests
Added unpublish action, added tests
Added tests
Merge branch 'unpublish' of git://github.com/ashleyconnor/django-publish into ashleyconnor-unpublish
Tidied up last few bits of unpublishing

Marking public foreign key as protected, so unpublishing (which is
basically delete) doesn't trample over everything.
Fixed test

As now redirecting to draft version if we go to public id in admin.
Version 0.4.0

Added "unpublish" action, which does slightly change schema (as set a
PROTECT on foreign key).