We broke xmlunit

[dsaff]

Apache Gump uses JUnit's trunk for everything it builds, but most of
the projects probably do't use assertThat at all.

One project that started to fail after you managed to get JUnit's
trunk compile on Java6 is xmlunit:

http://vmgump.apache.org/gump/public/xmlunit/xmlunit/gump_work/build_xmlunit_xmlunit.html

Since I'm the main developer of xmlunit right now, I was just about to
ping you anyway. So far I haven't found the time to look into the
root cause or even try to find a way of fixing xmlunit's build.