Fix issue with parent <- child Exposed instance relationship

This fixes an issue with namespaces to make the following work as
expected:

    app.expose('foo', 'window.foo');
    console.log(res.locals.state); // => window.foo = "foo";

    app.expose('bar', 'window.bar');
    console.log(res.locals.state); // => window.foo = "foo";

This also brings test coverage back to 100% and adds more code comments.