_clean_input_keys() does not follow RFC2109

[eluser]Derek Allard[/eluser]
This has come up recently. In response the input library now contains.

Code:

// Clean $_COOKIE Data
        // Also get rid of specially treated cookies that might be set by a server
        // or silly application, that are of no use to a CI application anyway
        // but that when present will trip our 'Disallowed Key Characters' alarm
        // http://www.ietf.org/rfc/rfc2109.txt
        // note that the key names below are single quoted strings, and are not PHP variables
        unset($_COOKIE['$Version']);
        unset($_COOKIE['$Path']);
        unset($_COOKIE['$Domain']);
        $_COOKIE = $this->_clean_input_data($_COOKIE);