[url] Fail quietly when finding out about a URL

[Stefano Rivera]

2009-05-30 17:40:05,691 ERROR plugins.url: Delicious logic - error determining the title for url http://explosm.net/coming
Traceback (most recent call last):
  File "/home/stefanor/projects/ibid/tibid/ibid/plugins/url.py", line 87, in _get_title
    etree = get_html_parse_tree(url, None, headers, 'etree')
  File "/home/stefanor/projects/ibid/tibid/ibid/utils.py", line 132, in get_html_parse_tree
    f = urllib2.urlopen(req)
  File "/usr/lib/python2.6/urllib2.py", line 124, in urlopen
    return _opener.open(url, data, timeout)
  File "/usr/lib/python2.6/urllib2.py", line 389, in open
    response = meth(req, response)
  File "/usr/lib/python2.6/urllib2.py", line 502, in http_response
    'http', request, response, code, msg, hdrs)
  File "/usr/lib/python2.6/urllib2.py", line 427, in error
    return self._call_chain(*args)
  File "/usr/lib/python2.6/urllib2.py", line 361, in _call_chain
    result = func(*args)
  File "/usr/lib/python2.6/urllib2.py", line 510, in http_error_default
    raise HTTPError(req.get_full_url(), code, msg, hdrs, fp)
HTTPError: HTTP Error 404: Not Found

I'm not sure we need to log these.