Changes to allow drush to run civimail and other crons

The following patch adds minor checks to see if civicrm is being called by drush, and if yes, does not include the civicrm.config.php (which is included with a relative path, so drush crashes, since it is not always in a specific directory).

For CRM/Utils/System/Drupal.php, it also simplifies the check (returns faster), since otherwise the path is similar to /var/foo/bar/drupalroot/, and then the function removes the last part, assuming that it is a php script.