[packagekit] Converted packagekit-glib2 to GDBus

[Richard Hughes]

I've just merged a mega-commit that ports libpackagekit-glib from
dbus-glib to GDBus.

There are no API or ABI changes in libpackagekit-glib, all the changes
are under the covers. I've not yet seen any regressions with the new
code, although the new code does feel a lot snappier in GUI programs.
Plus, cancellation now works reliably, which was the #1 reason to do
the port this week.

I would appreciate it if you guys could pull master and compile and
build the new code and then try to find bugs with client programs. I'm
sure I've broken something.

Thanks,

Richard.