RFR 9: 8143876 : test/java/lang/ProcessHandle/TreeTest.java failed intermittently with assertion error

[Roger Riggs]

Please review this change in ProcessHandle to validate parent pids 
provided by the OS.
Children of a process have start times that are the same or later than 
the parent.
The implementation of descendants(), and children(), and getParent()
are updated to validate the parent pid.

The problem is most pronounced on Windows; the parent pid reported for a
process may be stale if the parent exited.  The validation is applied in
platform neutral code and used on all platforms.  Platform specific code
is used on Windows for getParent(); the Linux platforms do the right thing.

Webrev:
    http://cr.openjdk.java.net/~rriggs/webrev-validate-ppid-8143879/

Issue:
    https://bugs.openjdk.java.net/browse/JDK-8143876

Thanks, Roger