Merge branch 'mh/write-refs-sooner-2.2' into mh/write-refs-sooner-2.3

* mh/write-refs-sooner-2.2:
ref_transaction_commit(): fix atomicity and avoid fd exhaustion
ref_transaction_commit(): remove the local flags variable
ref_transaction_commit(): inline call to write_ref_sha1()
rename_ref(): inline calls to write_ref_sha1() from this function
commit_ref_update(): new function, extracted from write_ref_sha1()
write_ref_to_lockfile(): new function, extracted from write_ref_sha1()
t7004: rename ULIMIT test prerequisite to ULIMIT_STACK_SIZE
update-ref: test handling large transactions properly

diff --cc refs.c
Simple merge

diff --cc t/t1400-update-ref.sh
Simple merge

diff --cc t/t7004-tag.sh
Simple merge