add image graph output (dot/graphviz)
add tests for 'images' subcommand
add doc for images -viz
packaging ubuntu; issue #510: Use goland-stable PPA package to build docker
Merge pull request #534 from dotcloud/510-update-go

* Packaging: packaging ubuntu; issue #510: Use goland-stable PPA package to build docker
Merge pull request #497 from justone/dot-graph-images

+ images: output graph of images to dot (graphviz)
Implement ENV within docker builder
Add the ENV instruciton to the docker builder documentation
Merge pull request #537 from dotcloud/builder-env

+ Builder: Implement ENV within docker builder