should <bits/unique_ptr.h> include <backward/auto_ptr.h>?

[Jonathan Wakely]

I'm working on std::wstring_convert and want to use std::unique_ptr.

To avoid <locale> pulling in the whole of <memory> I only want to
include unique_ptr.h, but that means I also need to include
<backward/auto_ptr.h>.  If bits/unique_ptr.h included auto_ptr.h
itself then we could just use unique_ptr.h elsewhere in the library
more easily.

Currently <future> includes the whole of <memory> but IIRC all it
really needs is unique_ptr.h, shared_ptr.h and allocator.h