Partially revert previous define-minor-mode change

* lisp/emacs-lisp/easy-mmode.el (easy-mmode--arg-docstring):
Only document the values we want to support, not the ones we
actually support.
(define-minor-mode): Partially revert to previous behaviour.

lisp/emacs-lisp/easy-mmode.el

@@ -90,7 +90,7 @@ the mode.
 
 If called from Lisp, toggle the mode if ARG is `toggle'.
 Enable the mode if ARG is nil, omitted, or is a positive number.
-All other values will disable the mode.
+Disable the mode if ARG is a negative number.
 
 The mode's hook is called both when the mode is enabled and when
 it is disabled.")
@@ -312,12 +312,10 @@ or call the function `%s'."))))
             (cond ((eq arg 'toggle)
                    (not ,getter))
                   ((and (numberp arg)
-                        (> arg 0))
-                   t)
-                  ((eq arg nil)
-                   t)
+                        (< arg 1))
+                   nil)
                   (t
-                   nil)))
+                   t)))
            ,@body
            ;; The on/off hooks are here for backward compatibility only.
            (run-hooks ',hook (if ,getter ',hook-on ',hook-off))