Combine month and year dropdowns for Views date filter

gistfile1.php

/**
 * Implements hook_date_select_process_alter().
 * Alter the month/year dropdown filter for views to use a single dropdown
 * instead of using separate year and month dropdowns.
 *
 * This is ONLY done on elements where #combine_dropdowns is TRUE on the
 * element. This is to prevent the process from being used on form elements
 * where it is not intended. Use form_alter to set #combine_dropdowns on form
 * elements that should use the combined dropdown.
 *
 * For more info, see hook_date_select_process_alter() documentation in
 * date.api.php of the contrib date module.
 */
function mymodule_date_select_process_alter(&$element, &$form_state, $context) {
  // Check the field name (usually date_filter, on Views)
  $field_name = $element['#parents'][0];
  $element_from_formvar = $context['form'][$field_name];

  // Check if this element should use combined Year/Month dropdown
  if (isset($element_from_formvar['#combine_dropdowns']) && $element_from_formvar['#combine_dropdowns']) {
    // Year/month dropdowns
    if ($element['#date_format'] == 'Y-m') {
      // Init the year and month values
      $year = $month = 0;

      // If the field already has values, use them
      if (isset($form_state['values'][$field_name]['value']['year_and_month'])) {
        $val = $form_state['values'][$field_name]['value']['year_and_month'];
        if (!empty($val)) {
          // Split the year and month
          list($year, $month) = explode('-', $val);
          if ($year > 0 && $month > 0) {
            // Save the values into the actual fields in form_state so it's used
            $form_state['values'][$field_name]['value']['year'] = $year;
            $form_state['values'][$field_name]['value']['month'] = $month;
          }
        }
      }

      // Build a combined year/month dropdown
      $values = array('' => t('<Any>'));
      foreach ($element['year']['#options'] as $y) {
        if ($y > 0) {
          foreach ($element['month']['#options'] as $mon_no => $mon_name) {
            if ($mon_no > 0) {
              if ($mon_no < 10) {
                $mon_no = '0' . $mon_no;
              }
              $values[$y . '-' . $mon_no] = $mon_name . ' ' . $y;
            }
          }
        }
      }

      // Add the new combined select
      $element['year_and_month'] = array(
        '#type' => 'select',
        '#options' => $values,
        '#default_value' => '',
        '#required' => FALSE,
      );

      // Nuke the Year and Month dropdowns, replacing with the actual values if
      // the filter has been submitted already
      $element['year'] = array(
        '#type' => 'value',
        '#value' => $year,
      );
      $element['month'] = array(
        '#type' => 'value',
        '#value' => $month,
      );
    }
  }
}