message: [C++] Add compile-time check to ProtocolReader
diff: #include <boost/mpl/list.hpp>
  #include <boost/mpl/push_front.hpp>
  #include <boost/mpl/copy_if.hpp>
  +#include <boost/mpl/contains.hpp>
  #include "customize.h"
  #include "detail/odr.h"
  @@ -185,7 +186,7 @@ struct ProtocolReader
  : value(x)
  {}
  - template <typename Reader>
  + template <typename Reader, typename boost::enable_if<boost::mpl::contains<typename Protocols<Buffer>::all, Reader> >::type* = nullptr>
  ProtocolReader(const Reader& reader)
  : value(reader)
  {}
  