Consider adding hooks for set/delete thumbnails.

[benhuson]

Hi

It would be useful to have something to hook into when a thumbnail is set/deleted.

I'm attempting to sync the setting of thumbnails in the WPML multi-language plugin and it would be handy to be able to set/delete thumbnails for translations when they are updated.

The pull request assumes using filters that include the thumbnail type ID:

delete_multi_thumbnail_{type_id}
set_multi_thumbnail_{type_id}

... and passing the $post_ID as a parameter, and $thumbnail_id as another parameter when setting an image.

Potentially having a more generic filter like delete_multi_thumbnail and passing $type_id as another parameter could work instead.

Ben

[chrisscott]

Thanks for the PR @benhuson! I'll take a look in the next few days.