Modify KVM to update guest time accounting.

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