[v3] C++11 allocator reqs for vector in debug & profile mode

[Paolo Carlini]

Hi
> I checked, and it's currently broken :)
>
> We do the wrong thing for allocators with propagate_on_container_swap==true.
>
> I think the fix might be as simple as constructing the new container
> with a copy of the old one's allocator, so even if it gets swapped
> it's equal.
>
> I'll deal with it asap.
Thanks a lot!

Paolo.