Merge branch 'jt/threaded-index-pack'

"git index-pack" learned to resolve deltified objects with greater parallelism. * jt/threaded-index-pack: index-pack: make quantum of work smaller index-pack: make resolve_delta() assume base data index-pack: calculate {ref,ofs}_{first,last} early index-pack: remove redundant child field index-pack: unify threaded and unthreaded code index-pack: remove redundant parameter Documentation: deltaBaseCacheLimit is per-thread