The standard is intentionally vague on if filesystems must
have '.' and '..' entries, allowing filesystems to omit this
concept completely:
http://pubs.opengroup.org/onlinepubs/9699919799/functions/readdir.html
However, the '.' and '..' entries are common on FAT filesystems
and in most other filesystems.
This enables '.' and '..' entries in the FAT filesystem.