Prior to this commit, `vagrant box prune --force` would not prompt a user to prune Vagrant boxes, even if that box was in use. There was no way to prune boxes, ignore the prompt, but keep in-use boxes. This commit adds a new flag that can be combined with `--force`, that will keep in-use boxes but prune older boxes without prompting the user.
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.