New action for wp_update_comment_count()

[mdawaffe]

wp_update_comment_count() calls the edit_post action (with different parameters than does the wp_insert_post() function), but this action doesn't receive information on how and if the count changed.

Knowing this information would be useful to advanced caching systems, plugins that do fancy things with plugins/pings, and surely a buch of stuff I can't think of.

I propose a new hook:

do_action('wp_update_comment_count', $post_id, $new_count, $old_count);

Attached makes that happen and gives the edi_post hook the same parameters as it has in wp_insert_post().

[ryan]

(In [5869]) wp_update_comment_count hook from mdawaffe. fixes #4740