[m-rev.] for review: Reduce use of foreign-exported procs in dir.m.

[Julien Fischer]

Hi Peter,

On Wed, 5 Oct 2016, Peter Wang wrote:

> Reduce use of foreign-exported procs in dir.m.
>
> library/io.m:
>    Note that io.system_error sometimes takes on Win32 error values.
>
>    Remove I/O state arguments on `make_err_msg' and
>    `make_maybe_win32_err_msg'.
>
>    Remove `was_error' argument from `ML_maybe_make_err_msg' and
>    `ML_maybe_make_win32_err_msg' macros, and rename the macros.

We should probably stop referring to it as "win32" and just
s/win32/windows/.

The diff looks fine.

Julien.