Merge branch 'jk/oid-array-cleanup'

Merge branch 'jk/oid-array-cleanup'

Code clean-up.

* jk/oid-array-cleanup:
  commit-graph: use size_t for array allocation and indexing
  commit-graph: replace packed_oid_list with oid_array
  commit-graph: drop count_distinct_commits() function
  oid-array: provide a for-loop iterator
  oid-array: make sort function public
  cache.h: move hash/oid functions to hash.h
  t0064: make duplicate tests more robust
  t0064: drop sha1 mention from filename
  oid-array.h: drop sha1 mention from header guard