backport of the Py3 stdlib subprocess module for Py2

 This is a backport of the Python 3.2 subprocess module to replace the stdlib
 subprocess module of Python versions 2.4 through 2.7, strongly recommended for
 POSIX systems. It includes a C extension used internally to handle the code
 path between fork() and exec(), which is more reliable when an application uses
 threads. Timeout support backported from Python 3.3 is also included. On the
 background, see PEP-324.