no prefork; no File::Type;

 * prefork is slow.
 * File::Type is too big and very slow.
 * It is sufficient to support the main file type
changelog for tokuhirom
v0.004

          replace File::Type with a much simpler and smaller-scale check
          (thanks, tokuhirom!)

          with File::Type gone, no need to use prefork anymore (thanks,
          tokuhirom!)