1.6.fix warnings

The code compiles now with -w Ae and -warn-error A.
I'm sure Mark would like to rewrite this ;-).
I haven't tested it, but doesn't
```
let is_ini_file path =
  try
    if (Unix.stat path).Unix.st_kind = Unix.S_REG
    then Filename.check_suffix path ".ini"
    else false
  with Unix.Unix_error (_,_,_) -> false in
```
(or sth along those lines) look more understandable?