Merge branch 'jc/maint-verify-objects-remove-pessimism'

The code to validate the history connectivity between old refs and new
refs used by fetch and receive-pack, introduced in 1.7.8, was grossly
inefficient and unnecessarily tried to re-validate integrity of individual
objects. This essentially reverts that performance regression.

* jc/maint-verify-objects-remove-pessimism:
  fetch/receive: remove over-pessimistic connectivity check