Merge branch 'md/filter-trees'

The "rev-list --filter" feature learned to exclude all trees via "tree:0" filter. * md/filter-trees: list-objects: support for skipping tree traversal filter-trees: code clean-up of tests list-objects-filter: implement filter tree:0 list-objects-filter-options: do not over-strbuf_init list-objects-filter: use BUG rather than die revision: mark non-user-given objects instead rev-list: handle missing tree objects properly list-objects: always parse trees gently list-objects: refactor to process_tree_contents list-objects: store common func args in struct