Re: [RFC 16/17] object_array_entry: copy name before storing in name field

> This is the culmination of the last few commits.  Since some callers
> want to store refnames in the name field of object_array elements, but
> we don't want those callers to assume that the refnames that they got
> from for_each_ref() have infinite lifetime, the easiest thing to do is
> have object_array make a copy of the names before writing them in the
> entries, and to free the names for entries that are no longer in use.
> This change fixes the problem, but has some disadvantages:
>
> * It requires extra copies to be made of strings that are already
>   copies, for example when the results of path_name(path, name) are
>   used as a name in revision.c:add_object().  This might be rare
>   enough that it can be ignored (though the original result of
>   path_name() would have to be freed, which this patch doesn't do so
>   there is a memory leak).
>
> * Many callers store the empty string ("") as the name; for example,
>   most of the entries created during a run of rev-list have "" as
>   their name.  This means that lots of needless copies of "" are being
>   made.  I think that the best solution to this problem would be to
>   store NULL rather than "" for such entries, but I haven't figured
>   out all of the places where the name is used.