Added unit tests for isWfUserAction() and checkUserAction(), and fixed a few bugs this way. Maybe we won't need getFreeVarsOfUserAction() after all.
Added test cases for the relatively new (public ...) and (secret ...) cases of UserKnowledge, and fixed a few bugs. We'd accidentally used "private" as the name of "secret".
Implemented and tested the (can ...) case for UserKnowledge.