More debugging... Entries and mime-types.

We now do a better job of determining what mime-type is preferred or required for a download, and/or defaulting to either application/octet-stream (if downloadable) or another download-link is there's only one choice.

Still need to debug reading larger files with a non-zero filesize, as well as displaced files. Aren't currently returning a stub on read. We're probably no longer implementing DisplacedFile calls completely.

TODO: We should also stop always writing stub files on explicity request. Just build and return the data, directly.