Add customisable OS to Vagrantfile

Choose the OS you want to run with the ALAVETELI_VAGRANT_OS environment
variable.

Examples:

    # Use default (Ubuntu 12.04 LTS (precise)
    vagrant up

    # Use Debian (7) Wheezy
    ALAVETELI_VAGRANT_OS=wheezy64 vagrant up
Use curl instead of wget in Vagrantfile

Use curl instead of wget in Vagrantfile to fetch the install script due
to a bug in the default version of wget on Debian Squeeze.

Fixes https://github.com/mysociety/alaveteli/issues/1691

> wget debian packages prior to 1.14-1 don't have SNI [1] support so the
> webserver don't know which ssl certificate needs to use
>
> – https://github.com/Hexxeh/rpi-update/issues/65#issuecomment-13332143
Update commonlib
Debian specific fixes

- Add wheezy repo to get bundler package which is
  unavailable in squeeze repo
- Get bundler from wheezy repo and de-prioritise all other
  wheezy packages
Add script to test vagrant vm provisioning

- e.g. script/test-vagrant-provisioning squeeze64
Update commonlib
Use official Canonical Ubuntu Precise image

Better source and includes curl
Precise specific fixes

- Get bundler and pdftk from raring repo and de-prioritise all other
  raring packages
Use our own Launchpad Ubuntu repo to get pdftk
Install the tools to install the tools!
Add -y option to install python-software-properties
Merge branch 'customisable-vagrant-box' into rails-3-develop