* gnus.el: Don't autoload "gnus-bitmap".

* gnus.el: Don't autoload "gnus-bitmap".

* gnus-sum.el (gnus-summary-toggle-smiley): Replace `gnus-smiley-display' with
 `gnus-article-smiley-display'.

* gnus-art.el (gnus-article-smiley-display): Re-implement to integrate smiley
 functions for various Emacsen.
(gnus-treatment-function-alist): Always use `gnus-article-smiley-display' for
 `gnus-treat-display-smileys'.
(gnus-treat-display-smileys): Use `gnus-image-type-available-p'.
(gnus-article-smiley-mule-loaded-p): New internal variable.
(gnus-article-should-use-smiley-mule): New user option.