title: Reuse property with version number when adding a dependency in sbt
body: <p>I have a project built with sbt 0.11.
  I'm trying to create a simple UI with Scala Swing, so first thing is to add a dependency on scala-swing in my build.sbt:</p>
  
  <pre><code>libraryDependencies += "org.scala-lang" % "scala-swing" % "2.9.1-1"
  </code></pre>
  
  <p>But I have a SettingKey scalaVersion defined:</p>
  
  <pre><code>scalaVersion := "2.9.1-1"
  </code></pre>
  
  <p>How can I reference that property? If I try to use it like</p>
  
  <pre><code>libraryDependencies += "org.scala-lang" % "scala-swing" % scalaVersion
  </code></pre>
  
  <p>Compiler complains that it found sbt.SettingKey[String] while String is expected. There are methods <code>get(...)</code> and <code>evaluate(...)</code> on SettingKey but they require some Setting[Scope] parameter to be passed in. </p>
  
  <p>What is the simplest way to just reference this property?</p>