Comment 9 for bug 2020000

Hi Simon,

I have added `Recommends: rust-doc` to the cargo-doc package.

After investigating and carefully considering the binary version situation, I decided to let the cargo binary package honour the rustc package version.
The reasonings are as follows:

- The Cargo crate version is only meant to be used when using Cargo as a library instead of a tool.
- Currently, Cargo and Rustc are released in sync; there will not be a situation where a new Rust release does not contain a new release of Cargo.
- Cargo, when building with Rustc, reports the Rustc version.

For the autopkgtest, I will remember to work on that after this merge.