Incoming files are matched against what is already stored, keyed on the
KOReader hash and the file size. Bulk uploads skip and report them, deliberate
creates are refused with a 409, the consume directory parks them aside, and
allow_duplicates overrides all three.
Also: books whose metadata generates a path another book already owns are moved
aside, so a forced copy cannot overwrite the original's files.
The filepath extractor was merged on the right, so a parent folder's name
overrode the title inside the file. Grouping also split a book's formats when
its own folder was the upload root.
file.path is relative to book.path, so the archive matched nothing on disk and
came out empty. Also namespace entries per book to stop filename collisions, and
stream the zip instead of buffering it whole.
The Darwin epub test cases used absolute paths. I hadn't notices until switching machines, whcih caused errors in the test harness. Changed to relative paths to be consistent with other test cases.