Use native scrollbar for navigation area

When the browser window is open long or resized often, the JavaScript scrollbar gets problems.  Also, the mouse wheel scrolling handler does not respect my customized scroll speed settings (Windows Control Panel).  What about using native scrollbars in this place?

![native-scrollbar](https://f.cloud.github.com/assets/157944/87728/4ae90ca8-64ce-11e2-8876-eb4acef36fbb.jpg)