Add tgz bundlescript

Closes #1675

Note that the exact URL for grabbing a specific version is changed from the old (and deprecated) "v" prefix intentionally, reflecting the change of the paths within from "docker-VERSION/docker" to "usr/local/bin/docker".

I was waiting for @shykes to review the tgz to make sure he was OK with the format, but I realized he can do that just as well (if not better) from a PR directly.

Here's some example output:
http://tianon-docker.s3.amazonaws.com/builds/Linux/x86_64/docker-0.6.6-dev.tgz
and/or
http://tianon-docker.s3.amazonaws.com/builds/Linux/x86_64/docker-latest.tgz