fixes CRM-13050

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* CRM-13050: cli.class.php doesn't import/export custom fields with multi-select values
  http://issues.civicrm.org/jira/browse/CRM-13050
Merge pull request #1227 from PalanteJon/for-real-2

fixes CRM-13050 - incorporates Kurund's suggestion to use  CRM_Core_DAO::VALUE_SEPARATOR