Fallback for finfo_open

Detect if the finfo_open function is available and if not, grab the file
extension and compare against an array to work out accepted text based
and image based file types to know wether to open in editor or pop open
as an image
Set $fileAtts to nothing as a fallback

Strict PHP modes will complain this isn't set otherwise
XAMPP needs more specific path

Possibly because index.php is calling lib/settings.php and this in turn
is calling config.php from it's location. Most web servers know you're
calling from the same dir but maybe XAMPP is thinking config.php should
be included from the index.php location? Anyway, fixed with a more
specific path.