function getParents(node) {
    var parent = node.parentNode;
    if(parent) return getParents(parent).concat(node);
    return [node];
}
Ordering test for any number of nodes - calls assertNodeOrder n-1 times.
Note that we only take the first matching node for each selector, and it's
not necessary that the nodes be siblings or at the same level of nesting.

@param {Array[string]} selectorArray: css selectors in the order they should
    appear in the document, from back to front.
@param {string} msg: context for debugging