Hello cargo

Built on top of https://github.com/rust-lang/rust/pull/15181. https://github.com/steveklabnik/rust/commit/e52719291183d7b4f691a1997c69fd75b8101b07 is the only new commit, you may want to review that separately.

I'm not sure if the car analogy is too glib.
You already have to trust Rust -- there's worse things that could happen, like the update.sh getting half run because your internet connection flaked out.

See http://blog.existentialize.com/dont-pipe-to-your-shell.html

IMHO you should download then execute the script in this guide

```sh
curl https://www.rust-lang.org/rustup.sh -o rustup.sh
sudo sh rustup.sh
```