Topic/scala fixes

This solves a couple of issues I ran into when developing the slick scaladays sample app.

* 8ca9fda bumps Scala version to 2.10.2 to avoid scalac typer crash with NPE
* 2308e2f adds type annotation to avoid existential type warning
* 6b0443d removes method overloading to avoid https://issues.scala-lang.org/browse/SI-7596

Be aware that 6b0443d breaks source compatibility for users, who used def Config.driver( ... ), but not for those that only imported or used val Config.driver .

I have no idea, why 919845a and 54a0755 appear in this pull request. Is this a github bug? Shouldn't be a problem for merging though.