create an API for interfacing with the Authorization Database
This is necessary to make UI like this http://people.freedesktop.org/~david/Screenshot-Manage%20Authorizations.png export some useful actions such as granting, revoking and displaying authorizations. Previously this API was internal, polkit/polkit-grant-database.[ch], and linked into polkit-grant(1) and libpolkit-grant(3) through a static library libpolkit-private.so. Only polkit-grant have not been ported; libpolkit-grant(3) uses this API natively now. Internally, right now, the new API just uses polkit-grant-database.[ch] directly but that is about to change...