Fix a parameter check. Thanks Lisandro Dalcin for the bug report.

More info @ http://www.open-mpi.org/community/lists/devel/2014/04/14561.php

cmr=v1.8.2:reviewer=ompi-rm1.8

This commit was SVN r31467.

ompi/mpi/c/op_commutative.c

@@ -46,7 +46,7 @@ int MPI_Op_commutative(MPI_Op op, int *commute)
     if (MPI_PARAM_CHECK) {
         OMPI_ERR_INIT_FINALIZE(FUNC_NAME);
         if (NULL == op ||
-            ompi_op_is_intrinsic(op)) {
+            !ompi_op_is_intrinsic(op)) {
             return OMPI_ERRHANDLER_INVOKE(MPI_COMM_WORLD, MPI_ERR_OP,
                                           FUNC_NAME);
         }