Merge branch 'jk/prune-mtime' into maint

Access to objects in repositories that borrow from another one on a slow NFS server unnecessarily got more expensive due to recent code becoming more cautious in a naive way not to lose objects to pruning. * jk/prune-mtime: sha1_file: only freshen packs once per run sha1_file: freshen pack objects before loose reachable: only mark local objects as recent