c++0x vs. tr1 type_traits, round 1

[Benjamin Kosnik]

> In general, these issue about TR1 vs C++0x are nasty. Other traits, for 
> example, are undergoing subtle semantic changes (for example, I 
> implemented __is_base_of consistently with the C++0x semantics and, as 
> you can see, for now, for TR1, I'm adjusting it a bit to the TR1 
> semantics); likewise for is_convertible_to, which will be different in 
> C+++0x (I'm currently working on the front-end support for it).

Also something that struck me as strange is that make_unsigned<wchar_t> 
gives unsigned wchar_t, but is_unsigned<wchar_t> doesn't work.

Either the algebra seems off, or my understanding is incomplete.

-benjamin