Merge branch 'jt/fetch-nego-tip'

Merge branch 'jt/fetch-nego-tip'

"git fetch" learned a new option "--negotiation-tip" to limit the
set of commits it tells the other end as "have", to reduce wasted
bandwidth and cycles, which would be helpful when the receiving
repository has a lot of refs that have little to do with the
history at the remote it is fetching from.

* jt/fetch-nego-tip:
  fetch-pack: support negotiation tip whitelist