[boost] [result_of] Regression: compilation errors on C++03 compilers when defining BOOST_RESULT_OF_USE_DECLTYPE

If we define BOOST_RESULT_OF_USE_DECLTYPE, boost::result_of tries to use decltype-based implementation even on C++03 compilers. This causes compilation errors and it is a regression on C++03 compilers. Is it intentional change? Regards, Michel