bug#4148: mode: for a minor mode should turn on, not toggle the mode

[Chong Yidong]

> A well known long standing problem:
> using 
> mode: SOME_MINOR_MODE

> in a local variable section (or in .dir-locals.el) toggles the minor
> mode, it should turn it on.

> So if the user sets a hook to turn on the minor mode in her emacs, when
> using a file that sets the same minor mode, the minor mode ends up being
> disable.

Does this patch DTRT?

*** trunk/lisp/files.el.~1.1066.~       2009-08-14 19:37:09.000000000 -0400
--- trunk/lisp/files.el 2009-08-15 13:37:24.000000000 -0400
***************
*** 3189,3195 ****
                                     "-mode"))))
           (unless (eq (indirect-function mode)
                       (indirect-function major-mode))
!            (funcall mode))))
        ((eq var 'eval)
         (save-excursion (eval val)))
        (t
--- 3189,3199 ----
                                     "-mode"))))
           (unless (eq (indirect-function mode)
                       (indirect-function major-mode))
!            (if (memq mode minor-mode-list)
!                ;; For a minor mode, enable unconditionally instead
!                ;; of toggling (since the mode may already be on).
!                (funcall mode 1)
!              (funcall mode)))))
        ((eq var 'eval)
         (save-excursion (eval val)))
        (t