Merge branch 'jt/fetch-pack-in-vain-count-with-stateless'

When "git fetch" tries to find where the history of the repository it runs in has diverged from what the other side has, it has a mechanism to avoid digging too deep into irrelevant side branches. This however did not work well over the "smart-http" transport due to a design bug, which has been fixed. * jt/fetch-pack-in-vain-count-with-stateless: fetch-pack: do not reset in_vain on non-novel acks