reset boot menu

[arne anka]

> Yes, probably something that we will need in the long run. Feel free to
> send me uBoot environment suggestions.

i do not really understand how u-boot works (i was surprised to learn that  
the actual menu resides on yet another partition).
but i think something like grub does would be nice:
- show boot menu by default
- hide the menu if configured, but show on button click (aux?)
- have a timeout and boot after that a default entry
- make configurable by config file like grub or rather lilo since it is  
written to a partition