Globalize `$blog_id` before loading WordPress
Globalize `$blog_id` before loading WordPress

Without `$blog_id` globalized, users with persistent object cache
drop-ins experience cache pollution.

```
vagrant@vip:/srv/www$ wp option get home
http://vip.local
vagrant@vip:/srv/www$ sudo service memcached restart
Restarting memcached: memcached.
vagrant@vip:/srv/www$ wp option get home
http://vip.local/fusion
vagrant@vip:/srv/www$ wp option get home --url=vip.local
http://vip.local/fusion
vagrant@vip:/srv/www$ sudo service memcached restart
Restarting memcached: memcached.
vagrant@vip:/srv/www$ wp option get home --url=vip.local
http://vip.local
```

Somewhere, there's usage of `$blog_id` in WordPress that should be
explicitly globalized, but isn't.

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