Use Scala 2.11 as default

* Improve cross build, so that test can be run with both 2.10 and 2.11
* Issue with multiple overloaded methods with default arguments,
  2.10 did not complain (strange)
* sbt 0.13.5
Merge pull request #57 from patriknw/wip-scala-2.11-patriknw

Use Scala 2.11 as default