* Don't create patches for archives >= 150 MB because bsdiff can't

  handle it.  It crashed on the 234 MB tetex archive.  Probably we
  will never be able to handle archives of that size on 32-bit
  machines (because bsdiff does everything in memory requiring
  max(17*n,9*n+m)+O(1) bytes, so the address space simply isn't
  there).