Merge branch 'am/xdiff-hash-tweak'

Inspired by Ezekiel's recent effort to showcase Rust interface, the
hash function implementation used to hash lines have been updated
to the one used for ELF symbol lookup by Glibc.

* am/xdiff-hash-tweak:
  xdiff: optimize xdl_hash_record_verbatim
  xdiff: refactor xdl_hash_record()