Part I of inline documenation for hooks in wp-includes/post.php.

Adds docs for the following hooks:
* `get_attached_file`
* `update_attached_file`
* `_wp_relative_upload_path`
* `post_type_labels_{$post_type}`
* `edit_{$field}`
* `{$field_no_prefix}_edit_pre`
* `edit_post_{$field}`
* `pre_{$field}`
* `{$field_no_prefix}_save_pre`
* `pre_post_{$field}`
* `{$field}_pre`
* `$field`
* `post_{$field}`
* `wp_count_posts`
* `wp_count_attachments`
* `post_mime_types`
* `wp_insert_post_empty_content`

See #25376.


git-svn-id: https://develop.svn.wordpress.org/trunk@28041 602fd350-edb4-49c9-b593-d223f7449a82