Definition of enforce-max-health in Chapter 4

The definition of "enforce-max-health" with keyword arguments does not work with the way it is called in the definition of "character".  This is an error in the book (page 190) and ch04-concurrency-repl-interactions.clj. However, the version in ch04-concurrency-game/src/com/clojurebook/concurrency/game_validators.clj is correct.
