When running `tox` on OSX as instructed at https://developers.home-assistant.io/docs/en/development_testing.html an error is received stating `error: [Errno 2] No such file or directory: 'autoconf': 'autoconf'`.
By installing `autoconf` via `homebrew`, this error goes away, and the `tox` tests pass. Telling OSX developers to install `autoconf` at this point in the development environment setup procedure (rather than calling it out on the testing page) seemed to make sense to me.
