Improve variants

[Mehdi Benharrats]

Hi,
I would be happy to help the bison project. I think I can improve the variant 
class to have a minimal alignment (and to assure its protability, which is 
currently not guaranteed), but I think I need some C++11 stuff to make things 
easier. So here comes the question : is it possible to use C++11 for this class 
? I can also write this class with a #if directive, thus the user will be able 
to use it only if he has a C++11 compiler.
If the answer is no, I will try to do it without C++11.
Thanks in advance for your answer.