States API doesn't work with multiple select fields

The States API won't pick up the value of a select field with #multiple = TRUE option.

Steps to reproduce:
- Create two fields in a form with the following code:

<?php
  $form['dependee'] = array(
    '#type'=> 'select',
    '#options'=> array(
      'a'=> 'Option A',
      'b'=> 'Option B',
      'c'=> 'Option C',
    ),
    '#multiple'=> TRUE,
  );

  $form['dependent'] = array(
    '#type'=> 'textfield',
    '#states'=> array(
      'visible'=> array(
        'select[name="dependee[]"]'=> array('value'=> array('a')),
      ),
    ),
  );
?>

The dependent field will stay hidden regardless of the value of the dependee. This happens because the value of a multiple select field is an array, and States tries to compare it with the reference with a === operator, which returns always false.

The proposed solution is to add a handler for arrays in states.Dependent.comparisons. This works with ANDed values:

'select[name="dependee[]"]' => array('value' => array('a', 'b')),

and with ORs as well (following the syntax proposed in #735528: FAPI #states: Fix conditionals to allow OR and XOR constructions):

'select[name="dependee[]"]' => array('value' => array('a')), array('value' => array('c'))