hash: make rotation more obvious

hash: make rotation more obvious

* modules/hash (Depends-on): Add bitrotate and stdint.
* lib/bitrotate.h (rotl_sz, rotr_sz): New functions.
* lib/hash.c (headers): Drop limits.h.  Add stdint.h.
(SIZE_MAX): Rely on headers for definition.
(hash_string) [USE_DIFF_HASH]: Use rotl_sz.
(raw_hasher): Use rotr_sz.
Suggested by Jim Meyering.

Signed-off-by: Eric Blake <ebb9@byu.net>