Scala 2.11 build for Scrooge-core

As requested in #129 and discussed with @mosesn in twitter/finagle#290 here's the Scala 2.11 support for scrooge-core.

As in the ScalaTest migration guide: http://www.scalatest.org/user_guide/migrating_to_20 I've updated the ScalaTest to 1.9.2 for Scala 2.9.x and 2.10.x and as there were no deprecations updated the dependency to 2.2.1 (newest stable version) for Scala 2.11.x.

As soon as there is a finagle branch cross compiled for Scala 2.11 I'll be able to work on all the other parts of Scrooge to support Scala 2.11.