dep.js: Set up `BAD' correctly.

Two bugs, which sort of cancelled each other out.

  * I failed to invoke `new' when I made `BAD', which meant that `BAD'
    actually ended up set to `undefined'.

  * I didn't set `DEP.val' properly if `value' wasn't passed explicitly,
    so, err, it ended up being `undefined', which is then erroneously
    considered to be equivalent to `BAD'.

Fix this silliness.