Re: [RFC PATCH 4/7] dir: Directories should be checked for matching pathspecs too

> Even if a directory doesn't match a pathspec, it is possible, depending
> on the precise pathspecs, that some file underneath it might.  So we
> special case and recurse into the directory for such situations.  However,
> we previously always added any untracked directory that we recursed into
> to the list of untracked paths, regardless of whether the directory
> itself matched the pathspec.
> 
> For the case of git-clean and a set of pathspecs of "dir/file" and "more",
> this caused a problem because we'd end up with dir entries for both of
>   "dir"
>   "dir/file"
> Then correct_untracked_entries() would try to helpfully prune duplicates
> for us by removing "dir/file" since it's under "dir", leaving us with
>   "dir"
> Since the original pathspec only had "dir/file", the only entry left
> doesn't match and leaves nothing to be removed.  (Note that if only one
> pathspec was specified, e.g. only "dir/file", then the common_prefix_len
> optimizations in fill_directory would cause us to bypass this problem,
> making it appear in simple tests that we could correctly remove manually
> specified pathspecs.)