support custom rootPath fixed #4

```js
    var app = connect(
      connect.cookieParser(),
      connect.session({
        secret: 'i m secret'
      }),
      // connect.query(),
      userauth(/^\/hello\/world\/user/i, {
        loginURLForamter: function (url, rootPath) {
          return rootPath + '/mocklogin?redirect=' + url;
        },
        rootPath: '/hello/world',
        getUser: function (req, callback) {
          process.nextTick(function () {
            var user = req.session.user;
            if (req.headers.mocklogin) {
              user = {
                nick: 'mock user',
                userid: 1234
              };
            }
            callback(null, user);
          });
        }
      })
    );
```