Drops 32bit in the Vagrantfile as well since we can build that with
gox and don't need a special environment for it. The Vagrantfile is
now just a good default development environment.
* Fixes up permissions so `make` runs cleanly after bringing up an environment.
* Adds better use of variables for Go paths.
* Adds a note about the ancient boxes.
* Silences wget spam while provisioning.