Fix an easy to trigger deadlock in std::io::stdio

Fix an easy to trigger deadlock in std::io::stdio

Being a person who somehow has taken a liking to premature optimisation, my knee-jerk reaction to
locking in std handles was preamble resembling following snippet:

    let stdout = stdout();
    let lstdout = stdout.lock();
    let stdin = stdin();
    let lstdin = stdin.lock();

and then reading from the locked handle like this:

    let mut letter = [0; 1];
    lstdin.read(&mut letter).unwrap();

As it is now this code will deadlock because the `read` method attempts to lock stdout as well!