Add originalRoute like originalUrl

In a request we can get the originalUrl, which is the complete URL for the request after it has travelled through nested routes.

But I think an originalRoute would be at least as usefull, especially for request logging.

I don't think it should be that difficult to add.

Currently I've made a simple hack to accomplish this, but I rather see it built-in.

```
var _ = require('lodash');
var express = require('express');
var Router = express.Router;
var Router_process_params = Router.process_params;

Router.process_params = function (layer, called, req, res, done) {
req.originalRoute = (req.originalRoute || '') + (req.route && req.route.path || layer.path || '');
return Router_process_params.apply(this, _.toArray(arguments));
}
```