Could you please tell me how to use the `magic_shell_environment` resource idempotently? Example: > install tomcat using ark cookbook (using `put` action that doesn't affect **$PATH**) > add tomcat to the **$PATH** Here's how I'm doing the second part: ``` tomcat_bin = tomcat_path + '/tomcat/bin' magic_shell_environment "PATH" do value tomcat_bin + ":$PATH" end ``` However, if I provision this script _n_ times, then my PATH contains _n_ tomcat instances added to the $PATH. Thanks