[v3] traits duplicate removal

[Paolo Carlini]

Benjamin Kosnik wrote:

>>Well, we could even have two specializations of the class, selected via 
>>__enable_if itself for integer and float types...
>>    
>>
>
>Yeah. But, then won't we have to drag in either tr1::traits or cpp_type_traits for is_integral?
>
Yes, actually I would use cpp_type_traits, which would not inject 
un-uglified names and it's rather small. An advantage of the solution is 
that, as often happens with Concepts (or its cheap replacements ;) 
normative text:

    // Only integer types.
    ...
    // Only floating point types.

would be replaced by actual code. But really, up to you.

Paolo.