Xen memory events: inspect Xen interface version to avoid compile failure on Xen 4.0.x. Improve logic in configure.ac and disable xen events by default. Xen events on 4.0.x are not unsupported.
Merge pull request #38 from smaresca/events_fix

Xen events build improvements
regression fix - xen_events.c : relocate ring page initialization to after enabling events. Without this change, commit 7defed7 caused a mem_event initialization failure on Xen 4.2.0.
Merge pull request #39 from smaresca/event_regression_fix

regression fix - xen_events.c : adjust order of operation for mem_events initialization
Allow building libvmi without xenstore
Merge pull request #40 from tklengyel/without-xenstore

Allow building libvmi without xenstore