Add support for sbt integration tests

Support for sbt integration tests as defined [here](http://www.scala-sbt.org/0.13/docs/Testing.html#Integration+Tests).
The basic idea is that the `IntegrationTest` scope trumps the `Test` scope when it exists.
jarSrcs is definitely needed. You can drop the `Docs` stuff, it's a far future feature to support loading the javadocs/scaladocs in emacs.