Updating core of a network install should go to upgrade sites

[defries]

When using WordPress as a network I think it's a miss when updating the core you're not being redirected to /wp-admin/network/upgrade.php as this clearly is the next step.

I realize that not every update will have a db change, but I'm guessing that can be filtered?

Even though this is specific to updating, changing component to Multisite so it will be on @petemall's report.

There has been some talk of merging upgrade.php with the unified updater. We can revisit this later if it is not addressed in 3.2.