noexcept for <tuple>. And in the process learned that I had done it wrong for...

noexcept for <tuple>.  And in the process learned that I had done it wrong for pair's swap.  I needed to create an __is_nothrow_swappable<T>::value trait that was smart enought to answer false when __is_swappable<T>::value is false.  Otherwise one gets compile-time errors when using pair or tuple of non-swappable types, even if you never try to swap the pair or tuple.

llvm-svn: 132204