portability enhancement: use "#!/usr/bin/env <interpreter>" on all perl scripts and shell scripts that use bash extensions, and use "#!/bin/sh" on the rest.

async-check.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 # This script creates symbolic links to the required asynchronous
 # file for using the asynchronous simulator and make check