[libvirt] [PATCH 1/1] Support for Callbacks and VirtualBox Version 3.

Hi All, I have added support for callbacks and VirtualBox version 3. I have attached the patch for the same, it is made against the head as of today. To check if the callbacks work you can run the example from examples/domain- events/events-c directory and then start a domain to see if you get any callback events. Regards, Pritesh