Fix build for building against Scala 2.11

- Allow building with local Scala version again.

- Upgrade to sbt 0.12.4 (0.12.3 is not compatible with Scala 2.11).

- Fix soundness problem in Shape with an explicit uncheckedVariance
  annotation (it should be sound the way we're using it but it is not
  sound in general and Scala 2.10 did not detect that).

- Change octal literals (deprecated in 2.11) to unicode literals

Review by @cvogt