`image-mode-fit-frame' doc fix

* image-mode.el (image-mode-fit-frame): Mention that it's a toggle
command

Fixes: debbugs:7729

lisp/ChangeLog

 2011-07-14  Lars Magne Ingebrigtsen  <larsi@gnus.org>
 
+	* image-mode.el (image-mode-fit-frame): Mention that it's a toggle
+	command (bug#7729).
+
 	* rect.el (apply-on-rectangle): Return the point after the last
 	operation.
 	(string-rectangle): Go to the point after the last operation

lisp/image-mode.el

@@ -271,7 +271,7 @@ stopping if the top or bottom edge of the image is reached."
 ;; Adjust frame and image size.
 
 (defun image-mode-fit-frame ()
-  "Fit the frame to the current image.
+  "Toggle whether to fit the frame to the current image.
 This function assumes the current frame has only one window."
   ;; FIXME: This does not take into account decorations like mode-line,
   ;; minibuffer, header-line, ...