Trim whitespace so parseHTML only contains HTML

On certain setups the checkout page never unblocks the payment portion of the page

If the server response to the AJAX form validation has leading whitespace, jQuery's .parseHTML will return an object with text nodes which when converted back to html using .html() results in *undefined*. Therefore the payment section is never updated.

Easy solution is to .trim() any whitespace before parsing the response.

http://jsfiddle.net/7XfYQ/