More stable and reliable way to set 'noValidate'

Setting 'novalidate' by `jQuery.attr` will throw `SCRIPT3: Member Not Found` exception in IE 7.

Coz standard browsers (IE 8 included) all support `form.noValidate`, and it's just setting a property to an object, IE 7 will not throw any exception, so can use `form.noValidate = true` instead jQuery way.

Demo and comparison: http://jsbin.com/iyoyam/2