hook_field_purge_field_instance() doesn't exist

While working on http://drupal.org/project/commerce_price_history, I found out the hard way (well, not really that hard) that hook_field_purge_field_instance() is actuallly hook_field_purge_instance().

Relevant part from field.crud.inc:

function field_purge_instance($instance) {
  ...
  // Invoke external hooks after the cache is cleared for API consistency.
  module_invoke_all('field_purge_instance', $instance);
}

Confusing part in field.api.php:

function hook_field_purge_field_instance($instance) {
  ...
}

Patch coming up in #1, `nuff said :)