Forcibly limit the duration of cached errors.

- CCP sends a cachedUntil value that is farther into the future for a
  request that should have succeeded normally when there is a temporary
  failure for any given API request, thus errors are cached far longer
  than they should have, resulting in needless failures.  The cache is
  updated to limit the damage this can do by lowering the duration to
  about an hour.

Fixes issue #1