Remove a compiler warning about an empty format string. The proper

way to have no abort message is to pass NULL (the errmanager is smart
enough to handle this case and not emit any extra message).

This commit was SVN r21311.

orte/mca/oob/tcp/oob_tcp.c

@@ -518,7 +518,7 @@ static void mca_oob_tcp_accept(int incoming_sd)
                     opal_output(0, "mca_oob_tcp_accept: accept() failed: %s (%d).", 
                                 strerror(opal_socket_errno), opal_socket_errno);
                 }
-                orte_errmgr.abort(ORTE_ERROR_DEFAULT_EXIT_CODE, "");
+                orte_errmgr.abort(ORTE_ERROR_DEFAULT_EXIT_CODE, NULL);
             }
             return;
         }