Enable altering of cid_parts in drupal_render_cid_parts

Current state:
Current block caching is limited per https://api.drupal.org/api/drupal/includes%21common.inc/group/block_cach...

Problem/motive:
I am having a need to cache block per IP. So I am proposing altering of drupal_render_cid_parts function $cid_parts array with drupal_alter.

With that you can edit granularity in your custom functions and add cid parts. Like I did here with help of Smart_IP module

define('DRUPAL_CACHE_PER_IP', 0x0005);
/**
 * Implements hook_cid_parts_alter().
 */

function lelo_performance_cid_parts_alter(&$cid_parts, &$granularity){

  if ($granularity & DRUPAL_CACHE_PER_IP) {
    $cid_parts[] = $base_root . request_uri() . $_SESSION['smart_ip']['location']['country_code'];
  }
}