add grant functionality + lots of other changes

add grant functionality + lots of other changes

 - Split libpolkit into three libraries
   - libpolkit : to be used only by mechanisms and modules
   - libpolkit-dbus : utility library for libpolkit to get caller, session
                      etc. info from the bus and ConsoleKit
   - libpolkit-grant : client side library for obtaining privileges; uses
                       a setgid helper internally

 - grant functionality
   - a helper library, libpolkit-grant, to gain privileges
     - includes a setgid $POLKIT_GROUP helper to write granted privileges
   - a PK module, to read and interpret granted privileges
   - a cmdline app, polkit-grant, using said library

 - Other changes
   - so it turns out that sizeof(bool) != sizeof(gboolean), sizeof(dbus_bool_t)
     This blows so define our own polkit_bool_t type
   - add some validation routines

The grant functionality, especially the setgid helper needs thorough
security review before we can release it.