Fix for fusion pair to make the compiler select the proper copy

constructor and remove a viable, but wrong, constructor. test added.

include/boost/fusion/support/pair.hpp

@@ -37,9 +37,11 @@ namespace boost { namespace fusion
             : second(rhs.second) {}
 
 #if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
+
         BOOST_FUSION_GPU_ENABLED
         pair(pair&& rhs)
             : second(std::forward<Second>(rhs.second)) {}
+
 #endif
 
         BOOST_FUSION_GPU_ENABLED
@@ -50,7 +52,7 @@ namespace boost { namespace fusion
 
         template <typename Second2>
         BOOST_FUSION_GPU_ENABLED
-        pair(Second2&& val
+        explicit pair(Second2&& val
           , typename boost::enable_if<is_convertible<Second2, Second> >::type* /*dummy*/ = 0
         ) : second(std::forward<Second2>(val)) {}