"Reinstall emails" tool fails on Network Admin

[needle]

Trying out the new features (nice work BTW!) and find that in multisite installs the "Reinstall emails" tool fails on Network Admin.

The cause is that [10536] prevents the taxonomy from being registered in Network Admin, so the terms are not created due to "Invalid taxonomy" errors.

[imath]

Thanks for your feedback @needle could you tell us how BuddyPress is activated ?

Is it network activated, or is it activated on a subsite ?

[needle]

@imath Sorry, should have said - network activated.

[DJPaul]

To clarify, the email posts are being added, but aren't being assigned to their taxonomies.

[DJPaul]

The tool function is bp_admin_reinstall_emails and it does have a switch_to_blog but clearly that doesn't internally switch registered taxonomies (TIL).

[DJPaul]

Patch registers the taxonomy when inside the network admin (which doesn't visually add any menus, because those are hidden), the existing switch_to_blog takes care of switching the tables, and everything ends up in the right place.

[DJPaul]

Fixing a bit differently -- using the pattern from r10580 instead. Tested, and it works.

[djpaul]

In 10581:

Emails: fix "reinstall emails" tool when run from Network Admin.

Similar to r10580, we needed to make sure the email type taxonomy is registered when we switch_to_blog to run the reinstall emails tool on the correct site.

Fixes #6891