* Treat major, minor numbers of HTTP version as separate integers
   * Fix errors if version string is "HTTP/1.2.3" or even simply "BLAH".
   * send_error() checks if 'self.command' is a
     HEAD.  However, if there's an error parsing the first line of the
     HTTP request the self.command wasn't set yet; force
     self.command to be initialized to None.