First sbt 0.13 test is passing.

* Migrate sbt version detection to common location.
* Modify shim installer so we can customize it by sbt version.
* Turn off all shim plugins for sbt 0.13 for now.
* Add sbt 0.13 support to the default sbt launcher.
* Add regular repositories for resolving in integration tests.
* Add scala-compiler 2.10.2 to cached resolution pool.
* Cried a little, to be honest.