RFR 9: 8129344 : (process) ProcessHandle instances should define equals and be value-based

[Roger Riggs]

Please review this update to ProcessHandle to specify the equals method
and that (JDK provided) instances have value-base semantics.

This update to the spec is needed to support pending work to uniquely
identify processes (8078099) using the process start time if available
from the operating system.

Wordsmithing may be needed.

Webrev:
    http://cr.openjdk.java.net/~rriggs/webrev-equals-8129344/

Issue:
   https://bugs.openjdk.java.net/browse/JDK-8078099

Thanks, Roger