Some changes and re-organization for animated gif support.

Some changes and re-organization for animated gif support.

* lisp/image.el (image-animate-max-time): Moved to image-mode.el.
(create-animated-image): Remove unnecessary function.
(image-animate): Rename from image-animate-start.  New arg.
(image-animate-stop): Removed; just use image-animate-timer.
(image-animate-timer): Use car-safe.
(image-animate-timeout): Rename argument.

* lisp/image-mode.el (image-toggle-animation): New command.
(image-mode-map): Bind it to RET.
(image-mode): Update message.
(image-toggle-display-image): Avoid a spurious cache flush.
(image-transform-rotation): Doc fix.
(image-transform-properties): Return quickly in the normal case.
(image-animate-loop): Rename from image-animate-max-time.