Re: [PATCH v3 0/5] fetch: implement support for atomic reference updates

> Changes compared to v2:
>
>     - `append_fetch_head` now takes a `struct object_id *old_oid`
>       instead of a `char *old_oid`.
>
>     - Handling of the merge status marker was moved into
>       `append_fetch_head`.
>
>     - I've unified code paths to format the line we're about to write to
>       FETCH_HEAD in atomic and non-atomic cases, which is the new 2/5
>       patch.
>
>     - We now always initialize `fetch_head->fp` and use it to derive
>       whether anything should be written at all instead of using the
>       global `write_fetch_head` variable.
>
> I think this should address all of Junio's feedback. Thanks for your
> input!