rust-status: only visit parts of the tree requested by the matcher This is an optimization that the matcher is designed to support, but we weren't doing it until now. This is primarily relevant for supporting "hg status [FILES]", where this optimization is crucial for getting good performance (without this optimization, that command will still scan the entire tree, and just filter it down after the fact). When this optimization fires we have to return false from traverse_fs_directory_and_dirstate, representing that that part of the tree *might* have new files which we didn't see because we skipped parts of it. This only affects the cached result of the status, and is necessary to make future status operations (which might use a different matcher) work properly.