[libvirt] libvirt-gconfig patches

Here is the 3rd version of my libvirt-gconfig patches, I did the renaming to put all the new classes it introduces in the GVirConfigDomain namespace. GVirConfigDomainSnapshot looks a bit out of place now though... Apart from this, I fixed the other issues that were reported, and rearranged a bit the patches introducing GVirConfigDomainInterfaceNetwork. I've also pushed the first 5 patches that were in v2 since they've already been ack'ed Christophe