Another workaround for MSVC variadic template bugs

https://connect.microsoft.com/VisualStudio/feedback/details/1045260/unpacking-std-forward-a-a-fails-when-nested-with-another-unpacking
Another MSVC 2013 variadic bug workaround

https://connect.microsoft.com/VisualStudio/feedback/details/1045260/unpacking-std-forward-a-a-fails-when-nested-with-another-unpacking