PDF generation with wkhtmltopdf on Windows does not work (easy fix)

On Windows, the stream_get_contents() on STDOUT gets blocked, with the result that the process never runs, no errors are generated, no files created...request just hangs.

The fix is to use 'append' mode in the descriptor argument element '2' for proc_open.

Here is the new line 382 of print_pdf_pages.inc:
$descriptor = array(0 => array('pipe', 'r'), 1 => array('pipe', 'w'), 2 => array('pipe', 'a'));
replacing this:
$descriptor = array(0 => array('pipe', 'r'), 1 => array('pipe', 'w'), 2 => array('pipe', 'w'));

This is the issue encountered:
http://www.php.net/manual/en/function.proc-open.php#97012
see also:
http://stackoverflow.com/questions/9024024/sometimes-wkhtmltopdf-windows...

I poked around the issues and could not find a dupe (sorry if there is one in there), but it does appear others may have reported on this but were unable to find the answer.

If you want me to generate a patch, let me know...it is changing one character in the file.