dev_settings: Add localhost:9991 as realm host for zulip realm.

[greg: Tweaked explanatory comment.]

zproject/dev_settings.py

@@ -21,6 +21,11 @@ if EXTERNAL_HOST is None:
         # For local development environments, we use localhost by
         # default, via the "zulipdev.com" hostname.
         EXTERNAL_HOST = 'zulipdev.com:9991'
+        # Serve the main dev realm at the literal name "localhost",
+        # so it works out of the box even when not on the Internet.
+        REALM_HOSTS = {
+            'zulip': 'localhost:9991'
+        }
 ALLOWED_HOSTS = ['*']
 
 # Uncomment extra backends if you want to test with them.  Note that

zproject/test_settings.py

@@ -18,6 +18,9 @@ if os.getenv("EXTERNAL_HOST") is None:
     os.environ["EXTERNAL_HOST"] = "testserver"
 from .settings import *
 
+# Clear out the REALM_HOSTS set in dev_settings.py
+REALM_HOSTS = {}
+
 # Used to clone DBs in backend tests.
 BACKEND_DATABASE_TEMPLATE = 'zulip_test_template'