Multisite loading is broken

```
salty-wordpress ➜  vip.dev  wp
PHP Fatal error:  Call to undefined function ms_subdomain_constants() in /srv/www/vip.dev/wp/wp-includes/ms-settings.php on line 18
```

Probably from https://core.trac.wordpress.org/changeset/28910/trunk/src
Travis fails it's running on older versions than trunk, and those older versions load the files again with `require()`