Department of Computer Science, University of Helsinki, Helsinki, PO Box 68, FIN-00014, Finland. Teemu.Kivioja@vtt.fi|Department of Computer Science, University of Helsinki, Helsinki, PO Box 68, FIN-00014, Finland. Teemu.Kivioja@vtt.fi|Department of Computer Science, University of Helsinki, Helsinki, PO Box 68, FIN-00014, Finland. Teemu.Kivioja@vtt.fi|Department of Computer Science, University of Helsinki, Helsinki, PO Box 68, FIN-00014, Finland. Teemu.Kivioja@vtt.fi|Department of Computer Science, University of Helsinki, Helsinki, PO Box 68, FIN-00014, Finland. Teemu.Kivioja@vtt.fi