Bug Report: SturdyRef doesn't have expiration date

[Mark S. Miller]

The most obviously offending piece of code is this in Registrar:

    /**
     * Produce a SturdyRef for an object.
     *
     * @param obj The object for which a SturdyRef is desired
     * @param expirationDate The date after which the SturdyRef will not
     *   longer be guaranteed to be valid
     *
     * @return A new SturdyRef for the indicated object
     */
    public SturdyRef makeSturdyRef(Object obj, Date expirationDate) {
        ObjectID objectID = register(obj, expirationDate);
        return new SturdyRef(this, myProxyManager.searchPath(), objectID);
    }

Also, class SturdyRef declares no state for representing the expiration
date.  However, EARL does have such state, and encodes/parses it to/from a
cap: URI.  Was it omitted from SturdyRef for a reason, or should I just fix it?