Automate release: settings for dependency versions.

Enable building against Scala 2.11.0-SNAPSHOT.

Disable `-Xfatal-warnings` to make PR validation less painful.
TODO: Re-enable for travis / nightlies.

TODO: Bump to Scala 2.11.0-M7, Scalacheck 1.11.0 once they're out.
Merge pull request #12 from adriaanm/master

Automate release: settings for dependency versions.