[v3 parallel mode] Parallel mode vs. movable

[Paolo Carlini]

Johannes Singler wrote:
> However, the error seems to appear inside the sequential sort routine. 
> The parallelized routine uses sequential sort, while the sequential 
> partial_sort does not. And AFAICS the movable test is switched off for 
> regular sort. So what's the current status? Is sequential "sort" 
> currently "movable-safe"?
I see. Indeed, std::sort isn't "moveable-safe" yet. I wanted to move 
over the v7-branch changes but seemed a bit invasive and heavy-handed, 
hopefully we can do that soon, now, in mainline. CC-ing Chris, in case 
he wants to help on that...

Paolo.