RFR: 8132541 : (process) ProcessBuilder support for redirection to discard output

[Roger Riggs]

Please review a proposed [1] ProcessBuilder addition to define a 
Redirect that will discard output.
The implementation is to redirect output to /dev/null or NUL on Windows.

Please review and comment if there are any unexpected side effects.

Webrev:
   http://cr.openjdk.java.net/~rriggs/webrev-8132541-discard/

Issue:
   https://bugs.openjdk.java.net/browse/JDK-8132541

Thanks, Roger

[1] 
http://mail.openjdk.java.net/pipermail/core-libs-dev/2015-July/034639.html