load LIMITED_DOMAINS from env var if available

for #1089

.gitignore

@@ -8,11 +8,6 @@ flask_secret_key
 /l
 /local*
 limited_domains
-make_password
 private_notes
 service_account_creds.json
-smtp_password
-smtp_user
-superfeedr_token
-superfeedr_username
 TAGS

protocol.py

@@ -2,6 +2,7 @@
 import copy
 from datetime import timedelta
 import logging
+import os
 import re
 from threading import Lock
 from urllib.parse import urljoin, urlparse
@@ -52,7 +53,8 @@ OBJECT_REFRESH_AGE = timedelta(days=30)
 
 # require a follow for users on these domains before we deliver anything from
 # them other than their profile
-LIMITED_DOMAINS = util.load_file_lines('limited_domains')
+LIMITED_DOMAINS = (os.getenv('LIMITED_DOMAINS', '').split()
+                   or util.load_file_lines('limited_domains'))
 
 # activity ids that we've already handled and can now ignore.
 # used in Protocol.receive