$config->resourceBase is not always correct

Although it seems this problem existed before, it has become more apparent because in CRM-11612 we standardized on using this for all resource loading.
It's been reported to be incorrect in the following situations:

• running Drupal under a path like http://localhost/drupal (fixed)
• in Joomla during the upgrade process - this may be a general problem during upgrade/install when $config is not being read from the db.