A complier bug related to overloading was causing boost signals2 and libraries that depend on signals2 to fail, so BOOST_NO_CXX11_VARIADIC_TEMPLATES was defined for VC++ 2013 as a sledge-hammer workaround. Now that the exact cause of the problem is known, BOOST_NO_CXX11_VARIADIC_TEMPLATES has been moved to the correct (i.e. pre-2013 RC) location. A specific workaround in signals2 will be applied separately.

[SVN r86408]