[tuple] default constructor for cons<>

From: David Abrahams (david.abrahams_at_[hidden])
Date: 2001-08-30 09:40:35

I have checked in a modification to boost/tuple/detail/tuple_basic.hpp on
the "rich_cons" branch which allows cons<> to be default-constructed.
Jaakko, I hope you find the changes acceptable and will merge them into the
main trunk. If there are any problems, please let me know.

Thanks,
Dave