This commits adds a new config setting `config.vm.box_server_url` to set the URL of a local VagrantCloud instance in the Vagrantfile. If the environment variable `VAGRANT_SERVER_URL` is set, it will still be preferred.
Vagrant Core Plugins
These are plugins that ship with Vagrant. Vagrant core uses its own plugin system to power a lot of the core pieces that ship with Vagrant. Each plugin will have its own README which explains its specific role.