Remove compression steps after ADD

When trying to run `build-all` I would get [an error about "invalid magic"](https://gist.github.com/BrianHicks/48845958101b93ae8958). After a little messing around with the Dockerfile, I found `ADD` instructions apparently *are* being decompressed from remote sources. The [docs for ADD](http://docs.docker.io/en/latest/use/builder/#add) say otherwise, however, so this may be a Docker bug.

> - If `<src>` is a local tar archive in a recognized compression format (identity, gzip, bzip2 or xz) then it is unpacked as a directory. Resources from *remote* URLs are **not** decompressed.