Merge branch 'jc/reflog-reverse-walk'

An internal function used to implement "git checkout @{-1}" was
hard to use correctly.

* jc/reflog-reverse-walk:
  refs.c: fix fread error handling
  reflog: add for_each_reflog_ent_reverse() API
  for_each_recent_reflog_ent(): simplify opening of a reflog file
  for_each_reflog_ent(): extract a helper to process a single entry

diff --cc refs.c
Simple merge

diff --cc refs.h
Simple merge

diff --cc sha1_name.c
Simple merge