mitchellh/vagrant — pull request #3538 by mitchellh (2014-04-24 17:38:02+00:00)
Title: Track box usage (local) to know if envs are using boxes

This PR adds the ability for Vagrant to know if other Vagrant environments are using boxes. We use this to warn users when you do a `vagrant box remove`. more importantly, this lays the foundation for what is required for linked clones.