Re: [PATCH 04/10] string-list API: mark "struct_string_list" to "for_each_string_list" const

> Add a "const" to the "struct string_list *" passed to
> for_each_string_list().
>
> This is arguably abuse of the type system, as the
> "string_list_each_func_t fn" take a "struct string_list_item *",
> i.e. not one with a "const", and those functions *can* modify those
> items.
>
> But as we'll see in a subsequent commit we have other such iteration
> functions that could benefit from a "const", i.e. to declare that
> we're not altering the list itself, even though we might be calling
> functions that alter its values.