allow multiple select in autocomplete

allow multiple select in autocomplete with updating of both display and
hidden fields

echo $this->Form->autocomplete('recipient', array(
					'type' => 'text',
					'label' => __d('croogo', 'Email Recipient'),
					'class' => 'span10',
					'autocomplete' => array(
						'default' => $username,
						'data-displayField' => 'name',
						'data-primaryKey' => 'email',
						'data-queryField' => 'name',
						'data-multiple' => 'true',
						'data-relatedElement' => '#CformRecipient',
						'data-url' => $UserEmailApiUrl,
					),
				));