Chage paginate.href(req) to use .originalUrl instead of url

If paginate.href(req) uses "url", it doesn't work when paginating inside routers.
For example:

```javascript
app.use(paginate(10,50));

var router = express.Router();
router.route("/list");

app.use("/myroute", router);
```

When accessing "/myroute/list", `paginate.href()` will return `<a href="/list?page=2&limit=10">Next</a>`, when it should return `<a href="/list?page=2&limit=10">Next</a>`.