v0.0.7

Only a few small changes here (although I've forgotten to tag some recent releases)

-- Prompt to the user when they use envy on a virtualenv that has already been backed up. This is important because if a user updates a version of a library (after having forgotten to run envy clean), and then uses envy again and this time remembers to run envy clean, they can end up with a stale version in their virtualenv.