Here is an updated version of @duckx code, it has the following improvements :
- only select the checkboxes of the label that has been clicked
- allows to toggle checkboxes
Drupal.behaviors.selectAll = {
attach: function (context, settings) {
$('body.page-node .form-type-checkboxes > label').click(function() {
$(this).nextAll('.form-checkboxes').find('input[type="checkbox"]').trigger('click');
});
}
};