[packagekit] Add support for package size and file list in description call

[Richard Hughes]

On Mon, 2007-10-01 at 22:04 -0400, Robin Norwood wrote:
> ** (process:19058): WARNING **: No marshaller for signature of signal
> 'Description'
> 
> And I'm not sure what I broke to cause it.

Ahh, you didn't update dbus_g_object_register_marshaller - I'll make
this change now and add some documentation.

Richard.