Add support for HAL-based hotplugging, in which we just get the list of
input devices and properties from HAL. Requires an FDI which is not yet
in mainline HAL.
Break up D-Bus into two components: a D-Bus core that can be used by any
part of the server (for the moment, just the D-Bus hotplug API, and the
forthcoming HAL hotplug API), and the old D-Bus hotplug API.
