Tell the users that they must run setup.sh after every webmin upgrade:
part of the setup procedure will insert the correct perl paths in the
webmin script, and webmin will not start without these settings.
This change allows webmin to be installed/upgraded using binary packages
only. A new pkg-message file will tell the user what to do to configure
webmin for the first time. The procedure is the same after both "make
install" and "pkg_add".