public function verbose($on = true, $output = STDERR)
{
// Turn off CURLINFO_HEADER_OUT for verbose to work. This has the side
// effect of causing Curl::requestHeaders to be empty.
if ($on) {
$this->setOpt(CURLINFO_HEADER_OUT, false);
}
$this->setOpt(CURLOPT_VERBOSE, $on);
$this->setOpt(CURLOPT_STDERR, $output);
}