Changes for clojure.core/defmulti

Victor on Mon, 22 Nov 2010
(defmulti service-charge (fn [acct] [(account-level acct) (:tag acct)]))
(defmethod service-charge [::acc/Basic ::acc/Checking]   [_] 25)
(defmethod service-charge [::acc/Basic ::acc/Savings]    [_] 10)
(defmethod service-charge [::acc/Premium ::acc/Account] [_] 0)