"git repack" used to write out unreachable objects as loose objects
when repacking, even if such loose objects will immediately pruned
due to its age.
By Jeff King
* jk/repack-no-explode-objects-from-old-pack:
gc: use argv-array for sub-commands
argv-array: add a new "pushl" method
argv-array: refactor empty_argv initialization
gc: do not explode objects which will be immediately pruned