Support for using vmfest images other than the default.

Default to installing a Vagrant Precise32, an Ubuntu 12.04 32bit image,
so it can be run by VBox installs incapable of running 64bit vms.

More reliable handling of images in general.
Update dependencies to released versions.
Add support for EC2. Vmfest detaults to ubuntu 12.04 vmfest image.
Merge branch 'develop' of https://github.com/pallet/learn-pallet into develop

Conflicts:
	src/learn_pallet.clj