For discussion! Enable compilation using Visual C++ 2002 & 2003

This bizarre patch results in a full test-suite pass for Visual Studio
.NET 2002 & 2003. Without it, the following code segfaults (resulting in
6 failing tests):

```ocaml
  #load "unix.cma";;
  let (ifd, _) = Unix.pipe ();;
  Unix.in_channel_of_descr ifd;;
```

otherlibs/win32unix/channels.c

@@ -46,6 +46,9 @@ CAMLprim value win_inchannel_of_filedescr(value handle)
   CAMLlocal1(vchan);
   struct channel * chan;
 
+#if defined(_MSC_VER) && _MSC_VER < 1400
+  fflush(stdin);
+#endif
   chan = caml_open_descriptor_in(win_CRT_fd_of_filedescr(handle));
   if (Descr_kind_val(handle) == KIND_SOCKET)
     chan->flags |= CHANNEL_FLAG_FROM_SOCKET;