Policy Middleware Doesn't Fire Default Error Handler

So if you pass an error to the policy middleware callback the default error handler attached to `sails.express.app.error` never fires due to the way the policy is called in the router.

example policy:

    module.exports = function(req, res, next) {
        next(new Error('foo bar'));
    };

This should fire the default blueprint error but it doesn't. Currently you have to manually send a response back if there is an error.

I have a patch for the router handler function in the policyRouter callback that will make it work but I want to add a test suite. I'll send a pull request in the next day or so after I figure out a good way to test the router.