Merge branch 'mv/maint-branch-m-symref'

* mv/maint-branch-m-symref: update-ref --no-deref -d: handle the case when the pointed ref is packed git branch -m: forbid renaming of a symref Fix git update-ref --no-deref -d. rename_ref(): handle the case when the reflog of a ref does not exist Fix git branch -m for symrefs.