Merge branch 'ps/fetch-optim'

Optimize code that handles large number of refs in the "git fetch" code path. * ps/fetch-optim: fetch: avoid second connectivity check if we already have all objects fetch: merge fetching and consuming refs fetch: refactor fetch refs to be more extendable fetch-pack: optimize loading of refs via commit graph connected: refactor iterator to return next object ID directly fetch: avoid unpacking headers in object existence check fetch: speed up lookup of want refs via commit-graph