Export custom fields of type country (regression)

Since the resolution of
CRM-17270 - Custom country multi-select fields used in a Drupal View display the four digit ID number instead of the name of the country we note a regression on export results for custom fields of type country.

Changes in this commit https://github.com/civicrm/civicrm-core/commit/9e39099940a94c91b9bd09aa1b241da72b0c482e affects on the data display for exports, showing only the country name of the the first row, and then showing the country id at the rest of rows.

We have applied the attached patch to recover the functionality as a workaround. The problem is generated at CRM/Export/BAO/Export.php at the line

$row[$field] = CRM_Core_BAO_CustomField::getDisplayValue($fieldValue, $cfID, $query->_options);

when getDisplayValue function overwrites $query->options at the first iteration.