CRM-10471 Drupal views: Filter civicrm contacts by current domain

In issue http://issues.civicrm.org/jira/browse/CRM-10457, I provided a patch which exposed the domain_id info of civicrm/drupal users in multisite environments.

In that ticket, I suggested a bit of additional work could be in providing a dedicated handler for domain_id filtering, such that you can select to filter by 'current id' rather than hard coding a domain id value.

The attached provides this handler.