need 2 binary libraries:
 libpw.a:	from s4util/* & s5/*
 comobj.a:	from com/*

programs stored in cmd/*
  "what" not used
  "delta" calls "bdiff" which calls "diff"
  "deltax" slightly modified "delta" which calls "diff" directly

the variable "difflim" inside "delta" is the number of lines
that "bdiff" passes to "diff" in each diff attempt
