"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