char_traits patch, round two

[Benjamin Kosnik]

> The standard does not have direct support for strings expressed as
> arrays of "unsigned char".  

Yep. The standard only specifies char and wchar_t specializations for
std::char_traits.

The correct way to deal with this now is to explicitly specialize
std::char_traits for user-defined types. That's always been the correct
way to deal with this, but the generic-mostly-correct definitions that
were previously in place allowed people to be lazy.

No more. 

-benjamin