Use /usr/bin/env in shebangs

Stop assuming that bash is in /bin, and that perl and python are in
/usr/bin, etc.
Instead, use env command to find these commands in the path.

client/gen_pm3mfsim_script.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 # Andrei Costin <zveriu@gmail.com>, 2011
 # gen_pm3mfsim_script.sh