source a setenv file when entering a bookmarked directory for the first time

In some directories I need to set up some environment variables before I can go on.
I therefore write simple scripts (called setenv.sh or setenv-source-me.sh) that set up
the correct environment for the current project.

Now when a bookmarked directory is visited (jumped to) for the first time in the current session, and if there is a file `setenv-source-me.sh` then this file will be sourced