Align sbt build for IDE and nightly build.

[Merge https://github.com/harrah/sbinary/pull/9 first!]

The only difference between the two builds is the vars section.
Ideally, these would be stored in properties file,
so that we can have only one dbuild config.

Build scalacheck (could also resolve it like scala-xml etc),
so we can run SBinary's test suite.

Also upgrade to M7 versions.properties.