Changes for grub-0.97-os.6 compared to os.5

- unsetall command
    - deletes all variables, frees all the internal variable memory
      useful to do in ones own menu at the start in case coming from
      another menu that already had variables set
- improve parsing, now things like this are possible
    title foo
    $(command)
- new built-in variable CLIENT_IP
- gcc4 build fixes (if it does not build with gcc4, please tell me)
- PXE-TFTP improvements
- print timeout upon "Press any key to continue" to see progress