[libvirt] [PATCH] Add some automatic dependency checks for configure to enable/disable {ESX, UML, LXC, Xen-Inotify}

Hi! While building libVirt on an older Debian Etch machine, I stumbled across some automatic enabled drivers which stopped configure and make very badly due to missing header files, old libraries and stuff. So I decided to improve the automagic tests so others won't face the same problem again :) Find four patches attached. Ciao Max -- Fortschritt bedeutet, einen Schritt so zu machen, daß man den nächsten auch noch machen kann.