Handles an OPTIONS request.

def do_OPTIONS(self):
        """Handles an OPTIONS request."""
        thread_local.clock_start = get_time()
        thread_local.status_code = 200
        thread_local.message = None
        thread_local.headers = []
        thread_local.end_headers = []
        thread_local.size = -1
        thread_local.method = 'OPTIONS'
        self.send_response(200)
        if self.is_cross_origin():
            no_caching = self.cross_origin_headers()
            # ten minutes if no custom headers requested
            self.send_header("Access-Control-Max-Age",
                             0 if no_caching else 10*60)
        self.send_header("Content-Length", 0)
        self.end_headers()
        thread_local.size = 0