More improvements to DEFINE-HASH-CACHE / DEFUN-CACHED

 - The :DEFAULT and :INIT-WRAPPER options are eliminated.
 - Any cache is immediately usable in cold-init.
   (Whether the underlying function works is a different issue)
 - The memoization wrapper is a little faster on a miss
   by avoiding recomputation of the hash for the missing entry.
 - To update a 1-arg/1-result function in the cache costs only 1 cons
   versus formerly 4 words for a 2-vector.