Accept a post object in clean_post_cache(). Fixes #20486.

The post_type can then be accessed to properly clean the taxonomy relationships cache.
The full object is useful in situations when an ID might reference a post that has been
removed from the database (e.g. wp_delete_post()).


git-svn-id: https://core.svn.wordpress.org/trunk@20569 1a063a9b-81f0-0310-95a4-ce76da25c4cd