"What's New" screen redirect confusing for update via network admin

[chipbennett]

When updating WordPress core via wp-admin/network, upon update completion, WordPress redirects to the "What's New" screen for the default site.

This redirect is confusing and counter-intuitive, because it takes the user from the network admin interface to the default-site admin interface. The default-site admin menu is displayed, rather than the network admin menu. Also, it requires the user to navigate back to the network admin, in order to perform the "update network" step.

I would recommend either replicating the "What's New" screen in the network admin interface (which would appear to require making about.php more context-aware, so that the network admin menu is displayed, rather than the default-site admin menu), or else not redirecting to the "What's New" page when updating via the network admin. The latter approach is probably more preferable, especially if the user is presented with an "update network" link upon successful core update.

Possibly related: #19737

It does know that the "Back to Updates" link should return to the network admin. But yes, this should be fixed.

In [19699]:

Create a network/about.php page and leverage it, to prevent the dashboard from switching to the blog admin. fixes #19762.

Note that is_network_admin() ? is used rather than self_admin_url() because there is not yet a wp-admin/user/about.php.

In [19700]:

about.php and friends for the global dashboard. see #19762.