the tests really prefer bash.

--- bison-3.0.4/examples/test.orig Tue Oct 20 10:07:20 2015

+++ bison-3.0.4/examples/test Tue Oct 20 10:07:25 2015

@@ -1,4 +1,4 @@

-#! /bin/sh

+#! /bin/bash

# Copyright (C) 2005-2015 Free Software Foundation, Inc.

#