DrupalAPCCache::set() expects a parameter Drupal will never pass

DrupalAPCCache::set() needs to have the same parameters used by DrupalCacheInterface::set(), but it has a parameter more, $headers, which will never be passed to DrupalAPCCache::set(). It was a parameter cache_set() had in Drupal 6, but it has been removed from Drupal 7.
DrupalAPCCache::set() also set $cache->headers with that parameter's value, but $cache->headers will not be used from Drupal core, nor from this module.

The $headers parameter must be removed from DrupalAPCCache::set(), which needs to stop setting $cache->headers.