The messages module contains message classes that can be added to a RPC response to provide additional information or warnings. This patch adds only the module with a single public message, VersionMissing, and unit tests. Since message classes are very similar to public errors, some functionality and unit tests were shared. Design page: http://freeipa.org/page/V3/Messages Ticket: https://fedorahosted.org/freeipa/ticket/2732