DirectoryIndexer: Handle Throwable

This skips classes which can't be loaded due to a SecurityException during
    the annotation pre-processing using the Eclipse Helper. Reason: Not all
    classes of a eclipse-plugin can't be loaded outside the eclipse-enviroment,
    i.e. from a "normal" java program. If you try to load them during
    annoation-preprocessing using the EclipseHelper, the SecurityException
    is thrown.