Add first and last classes to regions in Omega subtheme

/**
 * Implements hook_alpha_page_structure_alter().
 */
function YOURTHEMENAME_alpha_page_structure_alter(&$vars) {
  foreach (element_children($vars) as $section) {
    if (isset($vars[$section]['#section'])) {
      foreach (element_children($vars[$section]) as $zone) {
        _YOURTHEMENAME_calculate_first_last($vars[$section][$zone]);
      }
    }
  }
}

/**
 * Implements hook_alpha_preprocess_region().
 */
function YOURTHEMENAME_alpha_preprocess_region(&$vars) {
  if (!empty($vars['elements']['#grid']['first_column']) && $vars['elements']['#grid']['first_column'] == TRUE) {
    $vars['attributes_array']['class'][] = 'grid-first-column';
  }
  if (!empty($vars['elements']['#grid']['last_column']) && $vars['elements']['#grid']['last_column'] == TRUE) {
    $vars['attributes_array']['class'][] = 'grid-last-column';
  }
}

/**
 * Helper function to calculate which regions are positioned first and last
 * in the grid, within a given zone.
 */
function _YOURTHEMENAME_calculate_first_last(&$zone) {
  $regions = array();
  $sort_fields = array();
  $count = 1;

  foreach (element_children($zone) as $region) {
    $regions[] = $region;
    $sort_fields['position'][] = (!empty($zone[$region]['#position'])) ? $zone[$region]['#position'] : 0;
    $sort_fields['original_order'][] = $count;
    $count ++;
  }

  if (isset($zone['#data']['order']) && $zone['#data']['order'] == TRUE) {
    array_multisort($sort_fields['position'], $sort_fields['original_order'], $regions);
  }

  $columns = $zone['#data']['columns'];
  $current_position = 0;
  $previous_region = '';

  foreach ($regions as $region) {
    $total_width = $zone[$region]['#grid']['prefix'] + $zone[$region]['#grid']['columns'] + $zone[$region]['#grid']['suffix'];
    if ($current_position == 0) {
      $zone[$region]['#grid']['first_column'] = TRUE;
    }
    else if (!empty($previous_region) && $current_position + $total_width > $columns) {
      $zone[$previous_region]['#grid']['last_column'] = TRUE;
      $zone[$region]['#grid']['first_column'] = TRUE;
      $current_position = 0;
    }
    $current_position += $total_width;
    $previous_region = $region;
  }
  if (!empty($previous_region)) {
    $zone[$previous_region]['#grid']['last_column'] = TRUE;
  }
}