private static String toShortClassName(Object o) {
            String longName = o.getClass().getName();
            int lastDot = longName.lastIndexOf(".");
            if (lastDot < 0) return longName;
            return longName.substring(lastDot + 1);
        }
Returns a useful message from *this* exception, or null if none
configgen/src/main/java/com/yahoo/config/codegen/MakeConfig.java