Fix #598 by adding a boolean val typecheck.

Author: Kai Dorschner

src/rules.js

@@ -24,7 +24,7 @@ ko.validation.rules['required'] = {
 	validator: function (val, required) {
 		var testVal;
 
-		if (val === undefined || val === null) {
+		if (val === undefined || val === null || val === false) {
 			return !required;
 		}
 

test/rules-tests.js

@@ -16,6 +16,11 @@ QUnit.test('Object is NOT Valid and isValid returns False', function(assert) {
 	assert.violatesRequiredRule(testObj, '');
 });
 
+QUnit.test('Issue #598 - "false" is NOT valid and isValid returns false', function(assert) {
+	var testObj = ko.observable(false).extend({ required: true });
+	assert.violatesRequiredRule(testObj, '');
+});
+
 QUnit.test('Zero is a valid value for required', function(assert) {
 	var testObj = ko.observable(0).extend({ required: true });
 	assert.observableIsValid(testObj, 0);