[Patch] Use variadic templates for tr1::is_function

[Paolo Carlini]

Paolo Carlini wrote:

> Yes, that works fine, I know. Something I do *not* understand, 
> however, is why this does not work, what is so different about it:
>
>    typedef int (F)(double);
>
>    std::result_of<F(double)>::type

Ok, maybe now I see, in the latter case would make sense only 
result_of<F>::type, not result_of<F(double)>::type...

Hummm...

Paolo.