Changes to make the build work with Gradle 2.1 .

- Made methods which were called from afterEvaluate, as closures to work
  with Gradle 2.1 and the updated Groovy syntax.
- Fixed javadoc destinationDir
Use findbugs 2.0.2 on JDK 6 and lower.

- Latest findbugs runs only on JDK 7 and higher.