Merge branch 'jk/fetch-pack-remove-dups-optim'

The way "fetch-pack" that is given multiple references to fetch tried to
remove duplicates was very inefficient.

By Jeff King
* jk/fetch-pack-remove-dups-optim:
  fetch-pack: sort incoming heads list earlier
  fetch-pack: avoid quadratic loop in filter_refs
  fetch-pack: sort the list of incoming refs
  add sorting infrastructure for list refs
  fetch-pack: avoid quadratic behavior in remove_duplicates
  fetch-pack: sort incoming heads

diff --cc builtin/fetch-pack.c
Simple merge