ProcessBuilder support for pipelines

[Martin Buchholz]

Curmudgeon Martin supports this change!

I'm a little surprised we can implement it without native code.

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The below should probably be in its own paragraph.

+ * The {@link #startPipe startPipe} method can be invoked to create
+ * a pipeline of new processes that send the output of each process
+ * directly to the next process.  Each process has the attributes of
+ * its respective ProcessBuilder.

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I continue to be opposed to throwing UOE.  But it seems I've lost that
nano-argument.

+     * @throws  UnsupportedOperationException
+     *          If the operating system does not support the creation of
processes.

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These statements are technically incorrect.

+     * The standard output of all processes except the first process
+     * are <i>null output streams</i>
+     * The standard input of all processes except the last process
+     * are <i>null input streams</i>.

What you mean is that getOutputStream etc return null streams, but that's
not what you say.

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Should this mention standard error?

+     * @throws IllegalArgumentException any of the redirects except the
+     *          standard input of the first builder and the standard
output of
+     *          the last builder are not {@link Redirect#PIPE}.