avoid printing ghost location

Author: bobzhang

parsing/location.ml

@@ -239,6 +239,7 @@ let absolute_path s = (* This function could go into Filename *)
  aux s
 
 let show_filename file =
+ let file = if file = "_none_" then !input_name else file in 
  if !absname then absolute_path file else file
 
 let print_filename ppf file =