Updating nth_element for C++0x

[Paolo Carlini]

Hi,
>> 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?
> Whichever you have set on is fine.
Ok.
> That reminds me of another thing. With this patch, we now never use
> std::__median. However I left it in the code as it seems to be a
> documented SGI extension.
Let's leave it alone for now, I agree. At some point we may want to move
it to ext/algorithm, in namespace __gnu_cxx, together with all the other
extensions.

Paolo.