GUdev pygobject migration

Hi Felix!

I've been trying to use Udev Discover under openSUSE 12.1 and I turned into an issue. 
I know that actually, Udev Discover is partially ported to the new GObject Introspection based bindings, but gudev migration is missing, because it was not possible to get done  when the migration happened. Since pygobject doesn't support this situation from the 2.90.3 version, udev-discover needs this patch if we want to keep it working in newest distributions.

So, here's a patch! ;)
I've ported the remaining code, and all seems fine to me, but I have a question.

I removed the 'subsystems' argument while I'm getting some 'GUdev.Client' objects (see lines below)

-  self.client = gudev.Client(subsystems)
+ self.client = GUdev.Client()

Don't know the real impact of this, so it will be great if you make a review.

JFYI, I'm using GUdev from git (version 182) because there were some missing annotations, like the 'Device.get_parent' one. 

Best regards!