Merge branch 'jk/test-commit-bulk'

A test helper has been introduced to optimize preparation of test repositories with many simple commits, and a handful of test scripts have been updated to use it. * jk/test-commit-bulk: t6200: use test_commit_bulk t5703: use test_commit_bulk t5702: use test_commit_bulk t3311: use test_commit_bulk t5310: increase the number of bitmapped commits test-lib: introduce test_commit_bulk