Define nvp inside boost::serialization and bring it into boost

include/boost/core/nvp.hpp

@@ -12,6 +12,7 @@ Distributed under the Boost Software License, Version 1.0.
 #include <boost/config.hpp>
 
 namespace boost {
+namespace serialization {
 
 template<class T>
 class nvp {
@@ -37,6 +38,10 @@ private:
     T* v_;
 };
 
+} /* serialization */
+
+using serialization::nvp;
+
 template<class T>
 inline const nvp<T>
 make_nvp(const char* n, T& v) BOOST_NOEXCEPT