A bit OT but it would have been automatic if docker used a content-addressable filesystem to store the image content. Unfortunately `docker commit` is nothing l

A bit OT but it would have been automatic if docker used a content-addressable filesystem to store the image content. Unfortunately `docker commit` is nothing like `git commit` as it creates a differential snapshot of the filesystem. It unfortunate because now the user has to be careful not to insert a lot of data between steps in his Dockerfile or they will be shipped with the container even if removed by subsequent tests.