Why `C.ulong`? The API (http://libvirt.org/html/libvirt-libvirt.html#virDomainSetVcpusFlags) indicates the type `uint`, so cgo [won't build this](http://ci.serversaurus.com/github.com/alexzorin/libvirt-go/commit/7c750e1c9a7d98879057a204d640b97d27d4a483)