Function Request: Change Next/Previos Directory buttons.

```
Fast music folders navigaion while playing (like Car MP3 Receiver). This 
function will be useful in Car while driving.
I think, Up and Down DPad buttons is the best solution for this (instead 
volume boost).
```

Original issue reported on code.google.com by `freeusoft` on 6 Oct 2009 at 4:50
