Build fix for NetBSD and other systems where /bin/sh isn't bash

Fixed by explicitly using /bin/bash. Removing bash-isms would also
work. But /bin/sh is bash on most developers' systems, so using that
shell explicitly seems like it's less likely to break in the future.

test/run_tests.sh

@@ -1,4 +1,4 @@
-#!/bin/sh 
+#!/bin/bash 
 
 ECHO=`which echo`