[PATCH] Fix char_traits<wchar_t>::move

[Pétur Runólfsson]

> I'm going to commit this to both trunk and 3.3 as obviously correct in 
> the light of 21.1.1, p1 and Table 37.

I'm not sure that this is safe for 3.3, at least not on platforms
where wint_t and size_t are not the same type.

Petur