Got the same problem.
I removed the line (#518) and tried again - the install.php will showed the right screen after that...
I saw that my ISP runs PHP 4.X by default, which was the reason for that error.
After chaning to PHP 5.X and undoing my removed line everything worked fine.
Maybe you got the same prob - try to find out which PHP Version is running [for example by using phpinfo();]