get_cfg_var() might read wrong data - better use ini_get()

[MatthiasStolte]

I changed upload_max_filesize and post_max_size by a htaccess file, but get_max_file_size() in _include/fun_extra.php reads php.ini instead using runtime values. I replaced get_max_file_size() with ini_get() and now the correct setting is used.