document.observe("dom:loaded", function() {
    var f = $('filter_form');
    if (f) {
	f.descendants("input").each(function(input) {
	    input.observe('change', function(event) {
		formModified();
	    })
	})
    }
});

function formModified() {
    $('filter_submit').enable();
    $('filter_reset').enable();
}