Updated loader

[Peter Grehan]

http://www.ptree32.com.au/loader.120503

- accepts a single command-line parameter that can be used to set
  currdev

  e.g. 0 > boot enet:,loader hd:13

  or more usefully

       0 > boot hd:,loader hd:12

- fixed bug where a file offset > 4G was being truncated
- a colon wasn't being accepted as an indication of an OpenFirmware
   device. The symptom was that /etc/fstab wasn't being read in,
   resulting in the mountroot> prompt always popping up.

   This also allows device aliases to be used for disk specifiers
   at the loader prompt e.g.

   OK ls hd:12/boot

later,

Peter.