Merge branch 'jk/fetch-pack-many-refs'

Fetching between repositories with many refs employed O(n^2) algorithm to match up the common objects, which has been corrected. * jk/fetch-pack-many-refs: fetch-pack: avoid quadratic behavior in rev_list_push commit.c: make compare_commits_by_commit_date global fetch-pack: avoid quadratic list insertion in mark_complete