Merge branch 'jt/fetch-pack-negotiator'

Code restructuring and a small fix to transport protocol v2 during fetching. * jt/fetch-pack-negotiator: fetch-pack: introduce negotiator API fetch-pack: move common check and marking together fetch-pack: make negotiation-related vars local fetch-pack: use ref adv. to prune "have" sent fetch-pack: directly end negotiation if ACK ready fetch-pack: clear marks before re-marking fetch-pack: split up everything_local()