Added a warning about interfaces not implementable by users.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/math/trunk@1566416 13f79535-47bb-0310-9956-ffa450edef68
Configured rules for Clirr, as per discussion on the mailing list.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/math/trunk@1566417 13f79535-47bb-0310-9956-ffa450edef68