CRM-13027, CRM-12497 - Add test case for 'getfields' returning mismatched data


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* CRM-13027: Default getFields returns irrelevant custom-data fields
  http://issues.civicrm.org/jira/browse/CRM-13027
* CRM-12497: API 'getfields' method returns all custom fields
  http://issues.civicrm.org/jira/browse/CRM-12497