Internal dependencies fix

Hi,

Here is a fix I've come up with for issue #12 . I just add another fileset to the ant task for each directory in the  `internalDependencyClasspath` SBT key, so the compiled classes from the sub-projects get packaged together with the classes from the main project. External dependencies are not affected.

I have tested it in a small project with a few sub-projects, not all of them in the internal dependencies, and I haven't noticed anything weird. I may always have missed something of course.