One More Bit Of Pain

[Ori Bernstein <ori@xxxxxxxxxxxxxx>]

I have changed the usefile format. If you try building without cleaning the
old usefiles, you will get inscrutable errors and crashes.

You will have to update (in this order):
  - mc
  - libbio [you will have to use 'make', and not 'mbld' for this]
  - libregex [again, you will need to use 'make' and not 'mbld']
  - mbld [yep. you guessed it.]
  - everything else


This update adds an error for mismatched usefile versions,
so that in the future the need for this should become self
evident (and mbld will be able to cope with old usefile
versions).