Added new thread to read from subprocess's stdout

[exFalso]

Fixes https://github.com/prezi/gradle-haxe-plugin/issues/28

[exFalso]

If you read the stdout from the same thread that you forked the subprocess from, then your waitFor() call will hang, as nobody's reading the subprocess's stdout until it finishes, meaning a buffer will get full and the processes will deadlock.

The solution is to spawn a new thread that reads the subprocess's stdout while the original thread is blocking on waitFor().

References: http://stackoverflow.com/questions/3807834/processbuilder-gets-stuck-after-getting-an-error http://steveliles.github.io/invoking_processes_from_java.html

[lptr]

If you invoke waitFor() after reading the contents, it's okay. Have you tried this?

        Process process = builder.start();

        // remove it from here
        // process.waitFor();

        ByteArrayOutputStream bytes = new ByteArrayOutputStream();
        ByteStreams.copy(process.getInputStream(), bytes);
        String output = bytes.toString(Charsets.UTF_8.name());

        // move it to here
        process.waitFor();

[exFalso]

makes sense, https://github.com/prezi/gradle-haxe-plugin/commit/ee30f8602887788b06cac3da9387a062c74a92b3