new dependencies in gvfs

[Matthias Clasen <matthias clasen gmail com>]

David just merged the DeviceKit backend into gvfs, which means that
gvfs will now depend on gnome-disk-utility and DeviceKit-disks.

David will hopefully post something about some of the cool
things we get with this. This mail is more about the dry bureaucratic
aspects of this change...

The new dependencies are only conditional. The hal backend is still
there, so nobody will be rushed to switch to DeviceKit. Currently, the
new backend is built automatically when configure finds the necessary
dependencies, but there is a --en/disable-gdu option to force things.

I'd like to add the new dependencies to our list of external deps (and
to the jhbuild external-deps moduleset).

Comments ?

Matthias