Put jars for s.xml and s.u.parsing on classpath

As of Scala 2.11.0-M4, scala.xml and scala.util.parsing are
in [separate jars](https://github.com/scala/scala/issues/2704).

Improve `CompilerProvider` to deal with this in a backwards compatible way.
Merge pull request #22 from adriaanm/master

Put jars for scala.xml and scala.util.parsing on classpath for tests