[PATCH 0/7] merge-ort: implement support for packing objects together

(Based on the tip of 'eb/limit-bulk-checkin-to-blobs'.)

This series implements support for a new merge-tree option, `--write-pack`, which causes any newly-written objects to be packed together instead of being stored individually as loose.

The motivating use-case behind these changes is to better support repositories who invoke merge-tree frequently, generating a potentially large number of loose objects, resulting in a possible adverse effect on performance.

The majority of the changes here are preparatory to refactor common routines out of the bulk-checkin machinery to prepare for indexing different types of objects whose contents can be held in-core.

Also worth noting is the relative ease this series can be adapted to support the $NEW_HASH interop work in 'eb/hash-transition-rfc'. For more details on the relatively small number of changes necessary to make that work, see the log message of the second-to-last patch.

Thanks in advance for your review!

Taylor Blau (7):
  bulk-checkin: factor out `format_object_header_hash()`
  bulk-checkin: factor out `prepare_checkpoint()`
  bulk-checkin: factor out `truncate_checkpoint()`
  bulk-checkin: factor our `finalize_checkpoint()`
  bulk-checkin: introduce `index_blob_bulk_checkin_incore()`
  bulk-checkin: introduce `index_tree_bulk_checkin_incore()`
  builtin/merge-tree.c: implement support for `--write-pack`

 Documentation/git-merge-tree.txt |   4 +
 builtin/merge-tree.c             |   5 +
 bulk-checkin.c                   | 249 ++++++++++++++++++++++++++-----
 bulk-checkin.h                   |   8 +
 merge-ort.c                      |  43 ++++--
 merge-recursive.h                |   1 +
 t/t4301-merge-tree-write-tree.sh |  93 ++++++++++++
 7 files changed, 355 insertions(+), 48 deletions(-)