I got this error
  Fatal error: Call to a member function
  set_prefix() on a non-object in
  /home/reboltutorial/reboltutorial.com/wp-settings.php
  on line 254
line 254 contains:
$prefix = $wpdb->set_prefix($table_prefix); // set up global tables
This occurs if I try to call index_wordpress() instead of calling these two lines
    define('WP_USE_THEMES', true);  
    require('./wp-blog-header.php');  
so this doesn't work:
<?php
    function index_wordpress() {
        define('WP_USE_THEMES', true);  
        require('./wp-blog-header.php');  
    }
?>    
<?php
    if(!function_exists('apache_request_headers')) {
        function apache_request_headers() {
            $headers = array();
            foreach($_SERVER as $key => $value) {
                if(substr($key, 0, 5) == 'HTTP_') {
                    $headers[str_replace(' ', '-', ucwords(str_replace('_', ' ', strtolower(substr($key, 5)))))] = $value;
                }
            }
            return $headers;
        }
    }
    function getCurrentPageUrl() {
     $pageURL = 'http';
     if ($_SERVER["HTTPS"] == "on") {$pageURL .= "s";}
     $pageURL .= "://";
     if ($_SERVER["SERVER_PORT"] != "80") {
      $pageURL .= $_SERVER["SERVER_NAME"].":".$_SERVER["SERVER_PORT"].$_SERVER["REQUEST_URI"];
     } else {
      $pageURL .= $_SERVER["SERVER_NAME"].$_SERVER["REQUEST_URI"];
     }
     return $pageURL;
    }    
    $a =  apache_request_headers();
    $pos = strrpos($a["User-Agent"], "REBOL");
    if ($pos === false) {
        index_wordpress();
    } else {
      if ($_SERVER['REMOTE_ADDR'] != "69.163.203.14") {
        $command= './cgi-bin/index.cgi '. '"' . getCurrentPageUrl() . '"';
        echo system($command);
      } else {
        index_wordpress(); 
      }
    }
?>
while this works:
<?php
    if(!function_exists('apache_request_headers')) {
        function apache_request_headers() {
            $headers = array();
            foreach($_SERVER as $key => $value) {
                if(substr($key, 0, 5) == 'HTTP_') {
                    $headers[str_replace(' ', '-', ucwords(str_replace('_', ' ', strtolower(substr($key, 5)))))] = $value;
                }
            }
            return $headers;
        }
    }
    function getCurrentPageUrl() {
     $pageURL = 'http';
     if ($_SERVER["HTTPS"] == "on") {$pageURL .= "s";}
     $pageURL .= "://";
     if ($_SERVER["SERVER_PORT"] != "80") {
      $pageURL .= $_SERVER["SERVER_NAME"].":".$_SERVER["SERVER_PORT"].$_SERVER["REQUEST_URI"];
     } else {
      $pageURL .= $_SERVER["SERVER_NAME"].$_SERVER["REQUEST_URI"];
     }
     return $pageURL;
    }    
    $a =  apache_request_headers();
    $pos = strrpos($a["User-Agent"], "REBOL");
    if ($pos === false) {
        define('WP_USE_THEMES', true);  
        require('./wp-blog-header.php');
    } else {
      if ($_SERVER['REMOTE_ADDR'] != "69.163.203.14") {
        $command= './cgi-bin/index.cgi '. '"' . getCurrentPageUrl() . '"';
        echo system($command);
      } else {
        define('WP_USE_THEMES', true);  
        require('./wp-blog-header.php'); 
      }
    }
?>