(Originally suggested by James Henstridge in bug #897935)

There are also a few changes that would be nice to see
in pty.spawn:

1) get the exit status of the child. Could be fixed by
adding the following to the end of the function:
pid, status = os.waitpid(pid, 0)
return status

2) set master_fd to non-blocking mode, so that the
output is printed to the screen at the speed it is
produced by the child.