Backport of simple fix to not show negative CPU utilization. Bug: https://jbs.oracle.com/bugs/browse/JDK-6526682
Webrev: http://cr.openjdk.java.net/~nloodin/6526682/webrev.00/ Review thread: http://mail.openjdk.java.net/pipermail/serviceability-dev/2013-May/009976.html Checkin in JDK8: http://hg.openjdk.java.net/jdk8/tl-gate/jdk/rev/33d1376bf725 /Nils Loodin
