Merge branch 'jh/midx-verify-too-many-packs'

"git multi-pack-index verify" did not scale well with the number of packfiles, which is being improved. * jh/midx-verify-too-many-packs: midx: during verify group objects by packfile to speed verification midx: add progress indicators in multi-pack-index verify trace2:data: add trace2 data to midx progress: add sparse mode to force 100% complete message