Drop PostgreSQL superuser permissions after loading sample data
We don't use foi-purge-varnish ourselves, so remove it

We had various problems with the foi-purge-varnish script ourselves
that led to us removing it, so it seems like a bad idea to be
implicitly suggesting that others should use it.
crontab-example: use !!(*= .vhost_dir *)!! to avoid '/data/vhost/'

This is so that we can rewrite the crontab-example file into a real
crontab on systems where the prefix for virtual host directories
is something other than '/data/vhost'.
WiP: refactor version selection