man: Add MPI_DIST_GRAPH in MPI_TOPO_TEST manpage.

`MPI_DIST_GRAPH` was added in MPI-2.2.

ompi/mpi/man/man3/MPI_Topo_test.3in

@@ -65,6 +65,7 @@ The output value \fItop_type\fP is one of the following:
 .nf
     MPI_GRAPH		graph topology
     MPI_CART		Cartesian topology
+    MPI_DIST_GRAPH	distributed graph topology
     MPI_UNDEFINED	no topology
 
 .fi