Scala and sbt for Homebrew users

For Mac users who use Homebrew, this will get their Scala and sbt versions right:

git checkout 0e16b9d /usr/local/Library/Formula/scala.rb
git checkout d3206645661a149edc7b624b35772f344da0dc74 /usr/local/Library/Formula/sbt.rb
sbt install scala
sbt install sbt