Freak not out if classesDir doesn't exist.
Add create alias to apply for the Javas.

apply clashes with an instance name, so it's not promoted to a static method in
OptValue. Yay.
Make FeedbackException a runtime exception.

That way we can throw it from Java without fuss.
Add some bridges to Scala fns for the nonce.

The next Scala release may sufficiently improve SAM support that we can go back
to using Java fns everywhere, or not.