More robust URL-compare function

The trim-url function for comparing URLs to determine if they are "identical" (for purposes of displaying the URL following the text node for print outputs) is now more robust and ignores the following when determining "identicalness":

* Trailing forward slashes (e.g., "http://www.oreilly.com/")
* Opening www. not preceded by http:// (e.g., "www.oreilly.com")