Fix setting the max-upload-size for really large values.

php can only parse filesize units up to gigabytes, not terabytes or petabytes. The old code could add this
php_value upload_max_filesize 1000T
php_value post_max_size 1000T
to .htaccess, which gets parsed as 1000 Byte by PHP.

Please consider to merge this in the stable6 branch.