Merge branch 'ds/bsearch-hash'

Code to find the length to uniquely abbreviate object names based
on packfile content, which is a relatively recent addtion, has been
optimized to use the same fan-out table.

* ds/bsearch-hash:
  sha1_name: use bsearch_pack() in unique_in_pack()
  sha1_name: use bsearch_pack() for abbreviations
  packfile: define and use bsearch_pack()
  sha1_name: convert struct min_abbrev_data to object_id