title: Run sbt project in debug mode with a custom configuration
body: <p>I want to introduce a debug mode in my sbt 0.11 project using a special configuration.
  I've tried to implement this using the following code but unfortunately, it doesn't seems to work as expected. I'm launching <code>debug:run</code> but the run doesn't suspends as expected.</p>
  
  <pre class="lang-scala prettyprint-override"><code>object Test extends Build {
    lazy val root = Project("test", file("."))
      .configs( RunDebug )
      .settings( inConfig(RunDebug)(Defaults.configTasks):_*)
      .settings(
        name := "test debug",
        scalaVersion := "2.9.1",
        javaOptions in RunDebug += "-Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=5005",
        fork in RunDebug := true
      )
  
    lazy val RunDebug = config("debug").extend( Runtime )
  }
  </code></pre>