[PATCH][libstdc++-v3 parallel mode] Resolve namespace ambiguities

[Paolo Carlini]

Hi,
> This patch fixes ambiguities between __gnu_parallel and std that occur
> when the parallel algorithm are used selectively (i.e. without
> _GLIBCXX_PARALLEL).
>
> Tested x86_64-unknown-linux-gnu: No further regressions.
>
> Please approve for mainline and gcc-4_4-branch.
>   
The patch is Ok. Make sure you are never exceeding 80 columns before
committing.

Thanks,
Paolo.