Merge branch 'jk/reflog-walk-maint' into maint

After "git branch --move" of the currently checked out branch, the
code to walk the reflog of HEAD via "log -g" and friends
incorrectly stopped at the reflog entry that records the renaming
of the branch.

* jk/reflog-walk-maint:
  reflog-walk: include all fields when freeing complete_reflogs
  reflog-walk: don't free reflogs added to cache
  reflog-walk: duplicate strings in complete_reflogs list
  reflog-walk: skip over double-null oid due to HEAD rename