The traversal over tree objects has learned to honor
":(attr:label)" pathspec match, which has been implemented only for
enumerating paths on the filesystem.
* nd/attr-pathspec-in-tree-walk:
tree-walk: support :(attr) matching
dir.c: move, rename and export match_attrs()
pathspec.h: clean up "extern" in function declarations
tree-walk.c: make tree_entry_interesting() take an index
tree.c: make read_tree*() take 'struct repository *'