RFR 9: 8132883 : The spec of allChildren/children of j.l.Process/ProcessHandle need to be relaxed

[Roger Riggs]

Please review a couple of clarifications to the 
Process/ProcessHandle.allChildren methods.

8132883: Should not specify that non-alive processes have zero children.
        That is OS specific and cannot/should not be guaranteed by the spec
8131763:
   1. Requests a definition of 'direct' and 'indirect' children - direct 
children have the process as the parent
   2. Requests that the streams be specified as either sequential or 
parallel - the streams are sequential

Webrev:
    http://cr.openjdk.java.net/~rriggs/webrev-allchildren-8132883/

Issues:
    https://bugs.openjdk.java.net/browse/JDK-8132883
    https://bugs.openjdk.java.net/browse/JDK-8131763

Thanks, Roger