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

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