function cleanCssUrlQuotes(url) {
        //Make sure we are not ending in whitespace.
        //Not very confident of the css regexps above that there will not be ending
        //whitespace.
        url = url.replace(/\s+$/, "");

        if (url.charAt(0) === "'" || url.charAt(0) === "\"") {
            url = url.substring(1, url.length - 1);
        }

        return url;
    }
If an URL from a CSS url value contains start/end quotes, remove them.
This is not done in the regexp, since my regexp fu is not that strong,
and the CSS spec allows for ' and " in the URL if they are backslash escaped.
@param {String} url