Change codeigniter Log class to work with Raven-php

MY_Log.php

<?php

class MY_Log extends CI_Log {

    protected $_threshold	= 1;
    protected $_enabled	= TRUE;
    protected $_levels	= array('ERROR' => '1', 'DEBUG' => '2',  'INFO' => '3', 'ALL' => '4');
    protected $_raven_levels = array();
    protected $_client;

    /**
     * Constructor
     */
    public function __construct()
    {
        $config =& get_config();

        require_once APPPATH.'libraries/raven-php/lib/Raven/Autoloader.php';
        Raven_Autoloader::register();
        //Translates CI log levels to Raven log levels.
        $this->_raven_levels = array('ERROR' => Raven_Client::ERROR, 'DEBUG' => Raven_Client::DEBUG,  'INFO' => Raven_Client::INFO, 'ALL' => Raven_Client::DEBUG);
        // Instantiate a new client with a compatible DSN
        $this->_client = new Raven_Client($config['public_DSN']);

        $error_handler = new Raven_ErrorHandler($this->_client);
        $error_handler->registerExceptionHandler();

        if (is_numeric($config['log_threshold']))
        {
            $this->_threshold = $config['log_threshold'];
        }
    }

    // --------------------------------------------------------------------

    /**
     * Write Log File
     *
     * Generally this function will be called using the global log_message() function
     *
     * @param	string	the error level
     * @param	string	the error message
     * @param	bool	whether the error is a native PHP error
     * @return	bool
     */
    public function write_log($level = 'error', $msg, $php_error = FALSE)
    {
        if ($this->_enabled === FALSE)
        {
            return FALSE;
        }

        $level = strtoupper($level);

        if ( ! isset($this->_levels[$level]) OR ($this->_levels[$level] > $this->_threshold))
        {
            return FALSE;
        }
        $this->_client->captureMessage($msg,array(),$this->_raven_levels[$level],TRUE);

        return TRUE;
    }
}