Put sourceManaged files in a subdirectory found by sbt-idea

According to this thread "https://github.com/mpeltonen/sbt-idea/issues/209", generated files should be in a "main/pluginName" subdirectory of sourceManaged. Without this changes, sbt-idea will not add the generated files to the IntelliJ project.
Merge 227a1c9972fe041ea8ed124c94364efc0a99caf0 into fd9e5e6b6d96b9ef6a7af17996c58d479c388848
Change default Scala version to 2.9.2