[docs] [issue15561] update subprocess docs to reference io.TextIOWrapper

Chris Jerdonek added the comment: For 3.2 to mention write_through, issue 15638 should probably be fixed first. I can create a patch for that first. ---------- dependencies: +incorrect version info for TextIOWrapper write_through docs _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue15561> _______________________________________