* Add version number to bootstrap scripts.
* Always determine Bootstrap function and version.
* Write bootstrap version into venv.
* Add PrevBootstrapVersion function.
* Add OS bootstrapping check to phase 2.
* Differentiate -n and renew when rebootstrapping.
* Quote all environment variables.
* Correct test condition
* Add loud warning about hardcoded version list.
* s/VENV_BOOTSTRAP_VERSION/BOOTSTRAP_VERSION_PATH
* Properly handle noop bootstrap functions.