nth_element fix [58800]

[Paolo Carlini]

Hi,

On 10/19/2013 11:02 PM, Christopher Jefferson wrote:
> A previous fix to a performance problem in std::sort unfortunately has
> lead to a crashing bug in std::nth_element.
>
> The following minimal patch fixes the problem (there are a couple of
> different ways of fixing it, this is the shortest and safest).
>
> 2013-09-19 Chris Jefferson <chris@bubblescope.net>
>
> PR libstdc++/58800
> * include/bits/stl_algo.h (__unguarded_partition_pivot) : Change
> __last - 2 to __last - 1, so we correctly work on arrays of length 4.
> * testsuite/25_algorithms/nth_element/58800.cc : New
I have this already applied in my local svn branches and can apply it 
later today (I fixed the Copyright years to only 2013 of course and 
reformatted a bit the rest of the testcase)

Thanks!
Paolo.