Dynamically swaps an existing stylesheet reference for a new one
@param {String} id The id of an existing link tag to remove
@param {String} url The href of the new stylesheet to include
function(id, url) {
            var ss;
            CSS.removeStyleSheet(id);
            ss = doc.createElement("link");
            ss.setAttribute("rel", "stylesheet");
            ss.setAttribute("type", "text/css");
            ss.setAttribute("id", id);
            ss.setAttribute("href", url);
            doc.getElementsByTagName("head")[0].appendChild(ss);
        }