Using maven.jcoverage.instrumentation.exclude causes tests to fail

If you specify a file set that should not be instrumented using the 'maven.jcoverage.instrumentation.exclude' property your tests will fail if any of them depend on those files.

For example, I set 'maven.jcoverage.instrumentation.excludes=**/*Exception.class' so that my Exception classes would not be calculated in my code coverage stats. Unfortunately, my tests wouldn't run because all of my classes, including my test classes, rely on the Exception classes.

This is fairly critical for me, so I've attached a patch.