Fully transitive const is not necessary

[Janice Caron]

On 02/04/2008, guslay <guslay at gmail.com> wrote:
>  You have just made the mistake to assume that const implies thread-safe.

No I didn't. I stated that const is a /necessary/ condition for thread
safety, but nowhere did I claim it was a /sufficient/ condition.

I assumed (demonstrated, in fact), that mutable implies thread-unsafe,
but not that const implies thread-safe. There is a difference.