Copied maven/plugins/trunk/maven-pmd-plugin/src/it/MPMD-172 to maven/plugins/trunk/maven-checkstyle-plugin/src/it/MCHECKSTYLE-224.

git-svn-id: https://svn.apache.org/repos/asf/maven/plugins/trunk@1578334 13f79535-47bb-0310-9956-ffa450edef68
[MCHECKSTYLE-224] Warning about missing XRef for module with no source

- Add failing IT

git-svn-id: https://svn.apache.org/repos/asf/maven/plugins/trunk@1578344 13f79535-47bb-0310-9956-ffa450edef68