Comply with changes to Scala's branching

  - Explicitly use scala/scala#2.11.x as the git ref for Scala
  - Remove the GenBCode configuration. It has drifted out of date
    an we need to take another pass at it, hopefully finding a means
    to avoid duplication with the regular dbuild.
Merge pull request #36 from retronym/topic/branchy

Comply with changes to Scala's branching