procutil: introduce pseudo file object that just raises EBADF This should be safer than closing underlying fd as the fd may be reused. On Python 2, closed sys.stdin could be redirected to a random file having fd=0, but we'd be better not copying this behavior. Only readinto() and write() are implemented according to the following ABC table. fileno() is not implemented since fd=0/1/2 may be assigned later to other files. https://docs.python.org/3/library/io.html#class-hierarchy

dispatch: gate against missing stdout/stderr We do need procutil.stdin/stdout/stderr, but we don't care much for sys.std*. Let's leave them be None as it is the Python 3 way.