update for CrayL1 board

* Patch by Pantelis Antoniou, 21 Apr 2003:
  add boot support for ARTOS (a proprietary OS)

* Patch by Steven Scholz, 11 Apr 2003:
  Add support for RTC DS1338

* Patch by Rod Boyce, 24 Jan 2003:
  Fix counting of extended partitions in diskboot command