Record the realm of users in Mailchimp

THE CENSUS OF HUMBUG

Now it happened that at this time Waseem Daher issued a decree that
a census should be made of the whole users of Humbug.

This census -- the first -- took place while Faraone was governor of
MailChimp, and everyone went to be registered, each to his own realm.

So Alice Humbugger set out from the town of MIT for MailChimp in order to
be registered.

(imported from commit fca7714ebffd0b39b9b1337058f67975985f4039)

zephyr/views.py

@@ -251,6 +251,7 @@ def accounts_register(request):
                         'EMAIL': email,
                         'merge_vars': {
                             'NAME': full_name,
+                            'REALM': domain,
                             'OPTIN_IP': request.META['REMOTE_ADDR'],
                             'OPTIN_TIME': datetime.datetime.isoformat(datetime.datetime.now()),
                         },