入口文件APPPATH定义的问题，安装提示错误

叫我哀木涕

在lighttpd安装ci的时候提示错误：
[29-Jul-2013 14:18:34] PHP Warning:  require(application/config/constants.php) [<a href='function.require'>function.require</a>]: failed to open stream: No such file or directory in /home/users/mengrui/htdocs/www.ci.com/system/core/CodeIgniter.php on line 64[29-Jul-2013 14:18:34] PHP Fatal error:  require() [<a href='function.require'>function.require</a>]: Failed opening required 'application/config/constants.php' (include_path='/home/users/mengrui/bingo/php5/lib/php-libs/') in /home/users/mengrui/htdocs/www.ci.com/system/core/CodeIgniter.php on line 64

APPPATH为什么不用FCPATH . $app_folder   
看错误是require的时候用的是相对路径，出现错误。入口文件178行