Merge branch 'fixes'

* fixes:
  mpint: Fix misbehaviour on larger-than-mpw integer types.
  Fix various assumptions about mpw sizes.
  utils/mpreducetests.py: Tool to generate unpleasant mpreduce tests.
  mpreduce: Don't crash if we've accumulated no instructions.
  mpreduce: Don't stop bit scanner too early.
  mpreduce: Debug decomposition corrupts initial state for code generator.
  factorial: Fix usage message to fit in with conventions.
  cleanup: Various aesthetic fiddlings of little consequence.