More descriptive error message for invalid server

What steps will reproduce the problem?
$ ./upload.py -s google.com
Upload server: google.com (change with -s/--server)
New issue subject: Test
Traceback (most recent call last):
  File "./upload.py", line 2640, in <module>
    main()
  File "./upload.py", line 2632, in main
    RealMain(sys.argv)
  File "./upload.py", line 2588, in RealMain
    response_body = rpc_server.Send("/upload", body, content_type=ctype)
  File "./upload.py", line 446, in Send
    f = self.opener.open(req)
  File "/usr/lib/python2.7/urllib2.py", line 410, in open
    response = meth(req, response)
  File "/usr/lib/python2.7/urllib2.py", line 523, in http_response
    'http', request, response, code, msg, hdrs)
  File "/usr/lib/python2.7/urllib2.py", line 448, in error
    return self._call_chain(*args)
  File "/usr/lib/python2.7/urllib2.py", line 382, in _call_chain
    result = func(*args)
  File "/usr/lib/python2.7/urllib2.py", line 531, in http_error_default
    raise HTTPError(req.get_full_url(), code, msg, hdrs, fp)
urllib2.HTTPError: HTTP Error 404: Not Found

What is the expected output? What do you see instead?
Expected to show that "No Rietveld instance is found running at 
'http://google.com'"

Original issue reported on code.google.com by techtonik@gmail.com on 1 Jul 2013 at 11:48

gco / rietveld

More descriptive error message for invalid server #453