SBT 0.13 Support

I had to make this somewhat ugly change to scct for sbt-scct to work with sbt 0.13. `global.settings.outdir.value` returns null with sbt 0.13. Couldn't find anything in the sbt release notes to give a clue as to why this is.

Because this change only effects sbt 0.13, we only need it on `master` and not on the `2.9.2` branch (used for sbt 0.12)

Caveat: I haven't tested this change with a maven project yet, so I don't know what the impact of this change is for maven users.