Make pointcut pick up subclasses of ScalaJavaBuilder.

This fixes a problem at a customer (cleaning output folders, leading to
empty output folders after successful builds), but I could not reproduce
locally. Confirmed it works for said customer, so rolling back to main
project.
Merge pull request #599 from dragos/issue/pointcut-allow-subclasses

Make pointcut pick up subclasses of ScalaJavaBuilder.