Merge branch 'rs/ref-transaction-1'

The second batch of the transactional ref update series. * rs/ref-transaction-1: (22 commits) update-ref --stdin: pass transaction around explicitly update-ref --stdin: narrow scope of err strbuf refs.c: make delete_ref use a transaction refs.c: make prune_ref use a transaction to delete the ref refs.c: remove lock_ref_sha1 refs.c: remove the update_ref_write function refs.c: remove the update_ref_lock function refs.c: make lock_ref_sha1 static walker.c: use ref transaction for ref updates fast-import.c: use a ref transaction when dumping tags receive-pack.c: use a reference transaction for updating the refs refs.c: change update_ref to use a transaction branch.c: use ref transaction for all ref updates fast-import.c: change update_branch to use ref transactions sequencer.c: use ref transactions for all ref updates commit.c: use ref transactions for updates replace.c: use the ref transaction functions for updates tag.c: use ref transactions when doing updates refs.c: add transaction.status and track OPEN/CLOSED refs.c: make ref_transaction_begin take an err argument ...