[v3] Remove uses of <cstddef> as an implementation detail

[Paolo Carlini]

On 06/07/2010 08:56 PM, Martin Sebor wrote:
> Sorry for butting in, but wouldn't using gcc's __PTRDIFF_TYPE__
> and __SIZE_TYPE__ instead of the typedefs be cleaner (as in
> less public namespace pollution and stricter implementation)?
Indeed, we do that, we use those builtins, and we do that in namespace
std, per the discussion with Alisdair. In this way the users will still
be able to use std::size_t and std::ptrdiff_t, if, for some reason, they
are assuming that they can use those names because they see the names
used in the Standard in the exposition of those facilities. That cannot
hurt.

Paolo.