failErr is a failure by default, failInput is usage !379

failErr now answers not-found or failure; the former body is failInput, used by the call sites that validate the caller's own arguments. Store refusals (duplicate key, taken name, last admin, duplicate release or asset, org rename collision, reply to a reply) exit 1 instead of 2; the e2e assertions that pinned them follow. Under the JSON API those now map to 500 rather than 400. Stacked on !378. Closes #211.