Rewrite HashIndex using tuple_compare
Allow multipart hash in config checks (blueprint multipart-hash)
Add multipart hash tests
Add tests for search in NUM64 HashIndex using NUM key
tuple-compare-hash: review fixes

- simplify the comparison function, only shortuct the single-part
  NUM key case.
- tweak mh_find() declaration
- remove wrappers around hash values
  and keys
Merge branch 'tuple-compare-hash'