Merge branch 'jt/fetch-negotiator-skipping'

Add a server-side knob to skip commits in exponential/fibbonacci stride in an attempt to cover wider swath of history with a smaller number of iterations, potentially accepting a larger packfile transfer, instead of going back one commit a time during common ancestor discovery during the "git fetch" transaction. * jt/fetch-negotiator-skipping: negotiator/skipping: skip commits during fetch