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