Reduce option implementation in handler_filter_options

Wanted to limit the number of options in the select element to the selected one in filter settings form, that was not done so I did it.

Note :
In views original "in operator" filter handler I got most of the code from I saw this comment for the reduce method :
" // Because options may be an array of strings, or an array of mixed arrays
// and strings (optgroups) or an array of objects, we have to
// step through and handle each one individually."
As I was not sure we do need it in this views integration I did a much simpler reduce method, if I was wrong, feel free to let me know and I'll mostly copy / paste this method from original views handler.

I also did one cosmetic change :) "is one of " changed to "Is one of" as in original views handler (same for "Is not one ...").

Here is the diff (patch attached to issue):

12,13d11
< private $value_form_type = 'checkboxes';
<
19,20c17,18
< '=' => t('Is one of'),
< '<>' => t('Is not one of'),
---
> '=' => t('is one of'),
> '<>' => t('is not one of'),
25,83d22
< * Set reduce option to FALSE by default.
< */
< public function expose_options() {
< parent::expose_options();
< $this->options['expose']['reduce'] = FALSE;
< }
<
< /**
< * Define the form for exposed handler option reduce.
< */
< public function expose_form(&$form, &$form_state) {
< parent::expose_form($form, $form_state);
< $form['expose']['reduce'] = array(
< '#type' => 'checkbox',
< '#title' => t('Limit list to selected items'),
< '#description' => t('If checked, the only items presented to the user will be the ones selected here.'),
< '#default_value' => !empty($this->options['expose']['reduce']), // safety
< );
< }
<
< /**
< * Define reduce definition.
< */
< public function option_definition() {
< $options = parent::option_definition();
< $options['expose']['contains']['reduce'] = array('default' => FALSE);
< return $options;
< }
<
< /**
< * Reduce the options according the selection.
< */
< private function reduce_value_options() {
< $options = array();
< foreach ($this->definition['options'] as $id => $option) {
< if (isset($this->options['value'][$id])) {
< $options[$id] = $option;
< }
< }
< return $options;
< }
<
< /**
< * Save set checkboxes.
< */
< public function value_submit($form, &$form_state) {
< // Drupal's FAPI system automatically puts '0' in for any checkbox that
< // was not set, and the key to the checkbox if it is set.
< // Unfortunately, this means that if the key to that checkbox is 0,
< // we are unable to tell if that checkbox was set or not.
<
< // Luckily, the '#value' on the checkboxes form actually contains
< // *only* a list of checkboxes that were set, and we can use that
< // instead.
<
< $form_state['values']['options']['value'] = $form['value']['#value'];
< }
<
< /**
87,97d25
< $options = array();
< if (empty($form_state['exposed'])) {
< // Add a select all option to the value form.
< $options = array('all' => t('Select all'));
< }
< if (!empty($this->options['expose']['reduce']) && !empty($form_state['exposed'])) {
< $options += $this->reduce_value_options($form_state);
< }
< else {
< $options += $this->definition['options'];
< }
99c27
< '#type' => $this->value_form_type,
---
> '#type' => 'select',
101c29
< '#options' => $options,
---
> '#options' => $this->definition['options'],