Add timestamp to Client logs

[global-es]

Just add a timestamp to every log record in your Client.php:

    private function log($msg)
    {
        $msg = date('c') . "\t" . $msg;
	if (!$this->_debug) {
            return;
        }
        if (!$this->_logfile) {
            error_log($msg);
        } else {
            error_log($msg . "\n", 3, $this->_logfile);
        }
    }