Fix misspellings: whose instead of whos

Minor misspellings:

function user_rules_action_info() {
  return array(
    'rules_action_user_addrole' => array(
      'label' => t('Add user role'),
      'arguments' => array(
        'user' => array('type' => 'user', 'label' => t('User whos roles should be changed')),
      ),
      'module' => 'User',
    ),
    'rules_action_user_removerole' => array(
      'label' => t('Remove user role'),
      'arguments' => array(
        'user' => array('type' => 'user', 'label' => t('User whos roles should be changed')),
      ),
      'module' => 'User',
    ),
...

Both instances of "whos" should be "whose".