Querying button.value should return the value's attribute value

Firefox 1.x, Firefox 2.x, Firefox 3.x, Opera 9.25, Opera 9.50, Safari 3.0.4, Konqueror 3.5.8, Konqueror 4.1, Seamonkey 1.x, Seamonkey 2.x, NS 7.2, K-meleon 1.x, Galeon 2, Epiphany 2 all pass this test.