1.0.25.8: fix sxhash bug

1.0.25.8: fix sxhash bug

... brought to light by 1.0.20.27. Declare hashes to be of type HASH
(not INDEX).

Note that INDEX still is used to mean different things:

- a valid index: (integer 0 (array-dimension-limit))

- a "bound" such as the :START arguments: (integer 0 array-dimension-limit)

- a "dimension" as in (make-array 10): (integer 0 array-dimension-limit)

which leads to all kinds of nastiness with array near the limit.