1. Generate a correct Content-Length header visible through the info() method
   if a request to open an FTP URL gets a length in the response to RETR.

2. Take a third argument to urlretrieve() that makes it possible to progress-
   meter an urlretrieve call (this is what I needed the above change for).
   See the second patch band below for details.

3. To avoid spurious errors, I commented out the gopher test.  The target
   document no longer exists.