Modify KVM to update guest time accounting.

[ mingo@elte.hu: ported to 2.6.24 KVM. ]
Signed-off-by: NLaurent Vivier <Laurent.Vivier@bull.net>
Acked-by: NAvi Kivity <avi@qumranet.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>