Feature suggestion: duplicate detection

[aaazalea]

If someone uploads a puzzle that is already in the database, don't create multiple copies of it clogging up the home page.

[stevenhao]

this should be doable by maintaining something like puzzlehashes/:hash = {pid} in the db.

• the hash should not depend on metadata, because different sources (e.g. cruciverb archive page, nyt archive-view, downloadacross, nyt puzzle-view all provide .puz files, but all name the puzzles differently)

[stevenhao]

after detecting the duplicate, maybe we should a message like "this puzzle exists already" and show a link to /beta/play/:existingpid