On Ubuntu 12.04, I have installed typesafe-stack following the instructions [here](http://typesafe.com/stack/download).

After doing so, I do not have `scala` or `scalac` on my PATH. I do have `sbt`, and I can run `console` from there, but I do not have any native Scala executables installed.

Where is `scalac` supposed to be installed? Why has it not been so? How do I fix it?