Merge branch 'js/scalar-diagnose'

Implementation of "scalar diagnose" subcommand. * js/scalar-diagnose: scalar: teach `diagnose` to gather loose objects information scalar: teach `diagnose` to gather packfile info scalar diagnose: include disk space information scalar: implement `scalar diagnose` scalar: validate the optional enlistment argument archive --add-virtual-file: allow paths containing colons archive: optionally add "virtual" files