* filer: treat a directory carrying object data as an S3 key object
A file promoted to a directory by a child write keeps its chunks, inline
content, or remote-tiered entry. Recognize that as a directory key object,
not only when a Mime is set, so the object still lists, demotes on delete,
and is not reclaimed by cleanup like the object it still is.
* filer: keep the empty-folder cleaner from reclaiming a promoted object
The cleaner skips directory key objects, but its check only looked at the
Mime. Mirror the chunks/content/remote check so a file promoted to a
directory is not deleted once its children are gone.
* s3: serve ranged GET for a directory that carries object data
Reject only zero-size directories so a file promoted to a directory streams
range requests instead of returning 404, while empty directories still 404.
* s3: return HEAD metadata for a directory that carries object data
HEAD now 404s a directory only when it has no data, so a promoted object is
retrievable while empty/implicit directories still fall back to LIST.
Chris LuandGitHub
63f2f0bef5