Warn that non_blocking_any_source will fail with standard < 3.

test/non_blocking_any_source.cpp

@@ -25,6 +25,11 @@ test_main(int argc, char **argv)
   mpi::communicator world;
   int rank = world.rank();
   if (rank == 0) {
+#if BOOST_MPI_VERSION < 3
+    std::cout << "\nExpected failure with MPI standard < 3 ("
+	      << BOOST_MPI_VERSION << "." << BOOST_MPI_SUBVERSION
+	      << " detected)\n\n";
+#endif
     std::vector<boost::mpi::request> req;
     std::vector<std::vector<int> > data(world.size() - 1);
     for (int i = 1; i < world.size(); ++i) {