Implemented great suggestions from Jared Davis for improving our
original soundness bug fix, for CCL and (now) GCL with #+static-hons,
that called clear-memoize-tables when executing hons-wash.

- The fix now applies to hons-clear as well.  In fact our original
  proof of nil that exlpoited the hons-wash bug also applied with
  (hons-clear t) in place of hons-wash.

- For control-c safety, clear-memoize-tables is called as a first step
  in hons-wash and hons-clear.