Update PoliciesExpression to Policy config type

Fixes the bug mentioned in the mailing list (https://groups.google.com/d/msg/fubumvc-devel/qb1Uy5ePyWQ/zNFxvYGuEhwJ) since @mkmurray was working on other things.

I don't really like my tests though so I'd love if it could get some attention from @jeremydmiller @jmarnold or @CoreyKaylor to help me think of a better way to do this.