RFR 4483582: Process needs NIO channels to multiplex in/out/err

[Roger Riggs]

The changes to enable using Selectable channels with Process input and 
output got hung up
on an issue with the NIO Pipe implementation and behavior on Windows,  
the solution is elusive.

At this point, I would like to proceed with the implementation on Unix 
variants and come back
to the implementation Windows, possibly in JDK 9, possibly not.
The implementation on Windows throws an IOException on ProcessBuilder.start
if PIPE_CHANNEL redirection is selected in the builder.

Please take a look at the API and implementation for Unix and comment.

Webrev:
    http://cr.openjdk.java.net/~rriggs/webrev-pipe-selector-4483582/

Thanks, Roger