Problem:
Currently, only some filesystems (Btrfs, ext2, ext3, ext4) have full
support of accessing the `dirent` entry-type. On other filesystems,
`uv.fs_scandir_next` may return `nil` for an existing but unsupported
entry-type.
This means consumers (such as `fs.dir()`), cannot know if `nil` means
"non-existent" or "unsupported".
Solution:
Fall back to `uv.fs_lstat` when `etype` is `nil`; return "unknown" if it
fails.
(cherry picked from commit 4b5f026ac9)
b9d39f5bb2