We previously attempted to emit Rock Ridge NM records only when the name
represented by the Rock Ridge extensions would actually differ. We would
omit the record for an all-upper-case directory name, however Linux (and
perhaps other operating systems) map names with no NM record to
lowercase.

This affected only directories, as file names have an implicit ";1"
version number appended and thus always differ.  To solve, just emit NM
records for all entries other than DOT and DOTDOT .

We could continue to omit the NM record for directories that would avoid
mapping (for example, one named 1234.567) but this does not seem worth
the complexity.

From FreeBSD https://reviews.freebsd.org/D39258

(christos)