Dependency upgrades & a 2.11-only warning.

* Upgrade to scalaz 7.0.6.

* Upgrade to scalacheck 1.11.3 for non-2.9.2 builds.

* Add -Ywarn-unused-import for 2.11+ builds.

* Use sbt 0.13.1 and bintray-sbt 0.1.1.
Add Scala 2.11.0-RC1 build.