signup_views_default_views() is not re-entrant (causes fatal errors, missing views etc.)

I was debugging occasional fatal errors on a client site due to signup views going missing. I then put some debug in signup_views_default_views() and discovered that while it works the first time it's called, it then returns an empty array every subsequent time it's called later in the request.

This is just because it uses require_once instead of require, which means on subsequent runs, $view never gets set (because the file is not required again), so nothing gets returned.

Patch coming up once I have an nid.