osteosarc 0.14.3

Anyone can rebuild a bundle from its recipe (#89).

• A recipe's BAMs can be read through any snapshot that lists each one unchanged (the same URL, key, size and modification time as the recipe pins), not only through the snapshot it was made from, which only its builder had.
• osteosarc test-data make --recipe uses --snapshot if you give one, else the recipe's own snapshot if you have it, else your newest; it opens none when no BAM needs reading.