Merge branch 'tb/pack-bitmap-traversal-with-boundary'

The object traversal using reachability bitmap done by "pack-object" has been tweaked to take advantage of the fact that using "boundary" commits as representative of all the uninteresting ones can save quite a lot of object enumeration. * tb/pack-bitmap-traversal-with-boundary: pack-bitmap.c: use commit boundary during bitmap traversal pack-bitmap.c: extract `fill_in_bitmap()` object: add object_array initializer helper function