supporting deterministic 'ar'

[Cary Coutant]

> Alternatively, you could punt the problem to the user, and add a
> --timestamp=str option, where str is a getdate()-compatible date
> string. (And add --uid=n and --gid=n options as well. That would solve
> your problem of what to call the option.)

Oh, and what about the file mode? It's probably a good idea to force
that to a standard value (100444? 100644? 100640? 100600?).

-cary