Updating nth_element for C++0x

[Paolo Carlini]

Paolo Carlini wrote:
> I think __unguarded_partition_pivot should be inline, also all the
> function calls must be fully qualified with std, other than that the
> patch looks very nice to me. I'm going to apply it locally and give it a
> try.
>   
While testing a noticed you were unsure about __move_median_to_front vs
__move_median_first. For now I have here consistently the latter (patch
regtests fine). Is that name your preference?

Paolo.