canonicalizeHtml: allow spaces in attribute values
canonicalizeHtml: fix unquoted attribute values
throw error on triple-stache for attrs; fix tests
don't try to setAttribute 'type' for INPUT

IE8 doesn't let you set INPUT's type, even to the same value it already has.  When an element has reactive attributes, we set all the attributes when we get an invalidation, so there would be an error even if the type attribute was constant.  Now you only get an error if you actually try to change the type attribute from one thing to another.  In theory we could eventually support changing the type of an input by replacing the element (same as changing the contents of a STYLE element by replacing the element).