Support ocaml-compiler-libs v0.12.4

[cuihtlauac]

As of ocaml-compiler-libs v0.12.4 (required by repl.ml), module Toploop signature includes this:

    type input = Stdin | File of string | String of string
    val use_silently : Format.formatter -> input -> bool

This broke the way use_silently was used, line 111 (see issue #118)

This change fixes this.