Implement transactions for the packed ref store

This is v2 of a patch series to implement reference transactions for the packed refs-store. Thanks to Stefan, Brandon, Junio, and Peff for your review of v1 [1]. I believe I have addressed all of your comments.

Changes since v1:

* Patch [01/11]: justify the change better in the log message. Add a comment explaining why get_packed_ref_cache() is being called but the return value discarded.

* Patch [05/11]: Lock the packed-refs file *after* successfully creating the (empty) transaction object. This prevents leaving the file locked if ref_store_transaction_begin() fails.

* Patch [06/11]: New patch, fixing a leak of the refs_to_prune linked list.

* Patch [07/11]: Reimplement test "no bogus intermediate values during delete" to work without polling. Also incorporate Junio's change s/grep/test_i18ngrep/.

These changes are also available as branch packed-ref-transactions from my GitHub repo [2].

Michael

[1] https://public-inbox.org/git/[email protected]/
[2] https://github.com/mhagger/git

Michael Haggerty (11):
packed-backend: don't adjust the reference count on lock/unlock struct ref_transaction: add a place for backends to store data
packed_ref_store: implement reference transactions packed_delete_refs(): implement method
files_pack_refs(): use a reference transaction to write packed refs prune_refs(): also free the linked list files_initial_transaction_commit(): use a transaction for packed refs
t1404: demonstrate two problems with reference transactions
files_ref_store: use a transaction to update packed refs
packed-backend: rip out some now-unused code files_transaction_finish(): delete reflogs before references

 refs/files-backend.c         | 214 ++++++++++++++------
 refs/packed-backend.c        | 461 +++++++++++++++++++++++++++++--------------
 refs/packed-backend.h        |  17 +-
 refs/refs-internal.h         |   1 +
 t/t1404-update-ref-errors.sh |  73 +++++++
 5 files changed, 550 insertions(+), 216 deletions(-)

2.14.1