[Patch] Export __prime_list

[Benjamin Kosnik]

> I'd like to finally remove this hack too.

Sounds good to me. I'd meant to do this months ago: thanks for getting
to it.

It's a relief to get this stuff out of the headers, isn't it.

> In principle, we could also export a single list, but seems a tad
> cleaner to have separate copies in std::tr1::__detail and
> std::__detail and allow for the latter to be different. Anyway, if
> there are strong opinions, just let me know (for example, at some
> point I had a single list in __gnu_cxx...)

Looks fine to me. 

In general, I like the convergence toward
conceptually consistency, where tr1 and C++0x work is distinct. (We are
all on the same page here, but I thought I'd just say it.)

-benjamin