often, ftp URLs hang in the final close.  Further analysis suggests
that this is because the close hook in addclosehook() calls the hook
before acually closing the connection.  The hook, in this case, waits
for the '226 Transfer complete' status from the server on the command
socket.  However, more and more ftp servers only send this status when
the data socket has actually been closed -- causing a deadlock.

The fix is simple: in addclosehook.close(), call addbase.close()
*before* calling the closehook.