* Bail out on files that are too large earlier if possible.
* Return 400 instead of 500 for empty files and files that are too large
(when we can bail out early).
This new backend currently isn't hooked up; new and existing installs
will continue to use the localfs backend.
* Rework torrent generation to be backend-dependent so we can use S3's
existing torrent API.
* Remove the torrent test cases, which broke with this torrent rework;
they will need to be added back later.
* Use `http.MaxBytesReader` for better max size handling.
* Allow backends to return errors in `ServeFile` if needed.
mutantmonkey
mutantmonkey