Add install scripts for Alaveteli

site-specific-install.sh will be called by our generic site
install script in commonlib/bin/install-site.sh

These scripts assume that you have a new installation of
Debian squeeze or Ubuntu precise and then will set up:

 - Alaveteli running in development mode with the Thin web
   server behing nginx

 - The cron jobs that are required for the site to work.

 - A basic Postfix configuration for sending and receiving
   mail.

We also will use this script for generating new AMIs
(Amazon Machin Images) for Alaveteli.

The general.yml configuration file will be created if it
doesn't exist, but if there is an existing copy it won't be
overwritten, so it should be safe to customize that file and
then re-run the install script.
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