Show a better message on link-manager.php when links are disabled

[nacin]

We enforce the disabling of links via map_meta_cap(), since it's easy and clean. But it does mean that cap checks fail, which usually produces "You do not have sufficient permissions".

I meant to add a second message, but never did. Let's do that.

If we went all out, here's how I'd do it.

Are those localhost URLs in the patch correct?

Hah. Clearly not. :)

In multisite, a regular admin has manage_links but not install_plugins yet they still get a "please install" message that they cannot act upon themselves. Show the install message only if the user has both caps, otherwise the permissions error?

I think the call to user_can_access_admin_page() in wp-admin/includes/menu.php slams the door before these checks run.

Good points. 22569.3.diff​.

In 22855:

Show a better message ondmins on link-manager.php, link-add.php, link.php when links are disabled.

Props nacin
fixes #22569

Tested with super admin, normal admin, editor, and logged out.