wp_count_attachments() is not filterable

[kevinB]

The Media Library attachments listing and edit links can be filtered via existing WP_Query and has_cap hooks. However, corresponding attachment counts are not cleanly filterable.

[nacin]

Please create a diff from the checkout root. There are three different post.php files in core. :-)

[kevinB]

[updated] filter return value of wp_count_attachments()

[nacin]

In 25579:

Introduce a wp_count_attachments filter.

props kevinB.
fixes #17071.

[nacin]

In 25581:

Use correct variable. props helen. see #17071.