[libvirt] [RFC] making (newly public) EventImpl interface more consistent

[Ben Guthro]

>   I have no strong feeling w.r.t. the reregistration of an fd, I would
> rather error and not state it's undefined though.
>   For the java bindings, yes please :-) that way I would be able to
> push a new release too end of next week.

I'd like to get the Xen driver domain events in that release as well.
I'm working through some bugs with these, but I think it should be ready for review sometime this week, or beginning of next.