Method to automatically retrieve option labels CRM-12464

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* CRM-12464: Add PseudoConstants to Schema Metadata
  http://issues.civicrm.org/jira/browse/CRM-12464
Support "unique names" as well as sql name CRM-12464

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* CRM-12464: Add PseudoConstants to Schema Metadata
  http://issues.civicrm.org/jira/browse/CRM-12464