Working

<?php
//Added this function to emulate the one native in PHP 5.3
function get_called_class ()
{
    $t = debug_backtrace(); $t = $t[0];
    if ( isset( $t['object'] ) && $t['object'] instanceof $t['class'] )
        return get_class( $t['object'] );
    return false;
}

abstract class A_UserExporter{
    protected $users;
    protected $filename;

    protected $cols = array();
    protected $descriptions = array();


    public abstract static function getFileExtension();

    public abstract static function getFileExtensionDescription();

    protected abstract function printHeader();

    protected abstract function printFooter();

    protected abstract function printUser($user);

    public function __construct(array $users, $filename = ''){
        $_cols = array();
        $wpue_config = wpue_getConfig();
        if(isset($_POST['userdata']))
            foreach ($_POST['userdata'] as $col){
                $_cols[] = $col;
                $this->descriptions[$col] = $wpue_config->userdata[$col];
            }

        if(isset($_POST['metadata']))
            foreach ($_POST['metadata'] as $col){
                $_cols[] = $col;
                $this->descriptions[$col] = $wpue_config->metadata[$col];
            }

        if(wpue_isBP()){
            $bp_fields = wpue_bp_getProfileFields();
            foreach ($wpue_config->bp_fields as $field_id)
                if(isset($_POST['bp_fields']) && in_array($field_id, $_POST['bp_fields'])){
                    $col = 'bp_'.$field_id;
                    $_cols[] = $col;
                    $this->descriptions[$col] = $bp_fields[$field_id]->name;
                }

        }

        $this->users = $users;
        $this->filename = $filename ? $filename : 'users-'.date('Y-m-d');

        foreach($_POST['display_order'] as $field)
            if(in_array($field, $_cols))
                $this->cols[] = $field;
    }

    public final function export(){
        $this->printHeader();
        $keys = array_keys($this->users);

        foreach ($keys as $user_id){
            $user = $this->users[$user_id];
            $this->printUser($user);
            unset($this->users[$user_id]);
        }
        $this->printFooter();

        die;
    }


    public final static function activate(){
        $class = get_called_class();
        eval('$default = '.$class.'::getDefaultOptions();');
        $option = $class.'-options';
        if($default){
            if(get_option($option))
                delete_option($option);

            add_option($option, $default);
        }
    }

    public static function deactivate(){
        $option = get_called_class().'-options';
        if(get_option($option))
            delete_option($option);
    }

    //Then rewrite this to revent parse error in PHP < 5.3
    public static function saveOptions(){
       $class = get_called_class();
       $str = '$class::getPostedOptions()';
       eval("\$options = \"$str\";");
       $option = $class.'-options';
       if($options)
           update_option($option, $options);
    }

    public static function getOptions(){
        $option = get_called_class().'-options';
        return get_option($option);
    }

    public static function printOptionsForm(){}
    public static function getPostedOptions(){return null;}
    public static function getDefaultOptions(){return null;}
}