Merge branch 'ma/roll-back-lockfiles'

Some codepaths used to take a lockfile and did not roll it back; they are automatically rolled back at program exit, so there is no real "breakage", but it still is a good practice to roll back when you are done with a lockfile. * ma/roll-back-lockfiles: sequencer: do not roll back lockfile unnecessarily merge: always roll back lock in `checkout_fast_forward()` merge-recursive: always roll back lock in `merge_recursive_generic()` sequencer: always roll back lock in `do_recursive_merge()` sequencer: make lockfiles non-static