Merge branch 'ds/path-walk-1' into ds/backfill

* ds/path-walk-1: path-walk: drop redundant parse_tree() call path-walk: reorder object visits path-walk: mark trees and blobs as UNINTERESTING path-walk: visit tags and cached objects path-walk: allow consumer to specify object types t6601: add helper for testing path-walk API test-lib-functions: add test_cmp_sorted path-walk: introduce an object walk by path