vfs: treat 'undo.' file the same as 'journal.' file
They are the same kind of file, they are protected by the store lock, but
directly lives inside the '.hg' directory.
No warnings were ever raised about them because `vfs.rename` is not audited.
Something we are trying to change.
<tr>
<td class="diffstat-file"><a href="#l{fileno}.1">{file|escape}</a></td>
<td class="diffstat-total" align="right">{total}</td>
<td class="diffstat-graph">
<span class="diffstat-add" style="width:{addpct}%;"> </span>
<span class="diffstat-remove" style="width:{removepct}%;"> </span>
</td>
</tr>