function bound() {
            return callback.apply(thisp, arguments);
        }
If a function would like to support both Node continuation-passing-style and
promise-returning-style, it can end its internal promise chain with
`nodeify(nodeback)`, forwarding the optional nodeback argument.  If the user
elects to use a nodeback, the result will be sent there.  If they do not
pass a nodeback, they will receive the result promise.
@param object a result (or a promise for a result)
@param {Function} nodeback a Node.js-style callback
@returns either the promise or nothing