dotcloud/docker — pull request #1667 by mhennings (2013-08-25 20:44:13+00:00)
Title: Allow an override for the FROM line in Dockerfile

Docker build gets an option to override FROM
This makes reuse of Dockerfiles easier.

Example:

docker build -t mhennings/ubuntu-chef -b ubuntu .

The from line in the Dockerfile is ignored instead "ubuntu" is used as the
value for FROM