Change initial migration writing to work as docs suggest.

Application template now includes an empty migrations module, and
the autodetector will only make initial migrations for apps with
empty modules.

django/db/migrations/autodetector.py

@@ -1,6 +1,7 @@
 import re
+import os
 import sys
-from django.utils import datetime_safe
+from django.utils import datetime_safe, importlib
 from django.utils.six.moves import input
 from django.db.migrations import operations
 from django.db.migrations.migration import Migration
@@ -410,15 +411,22 @@ class InteractiveMigrationQuestioner(MigrationQuestioner):
 
     def ask_initial(self, app_label):
         "Should we create an initial migration for the app?"
-        # Don't ask for django.contrib apps
-        app = cache.get_app(app_label)
-        if app.__name__.startswith("django.contrib"):
-            return False
         # If it was specified on the command line, definitely true
         if app_label in self.specified_apps:
             return True
-        # Now ask
-        return self._boolean_input("Do you want to enable migrations for app '%s'? [y/N]" % app_label, False)
+        # Otherwise, we look to see if it has a migrations module
+        # without any Python files in it, apart from __init__.py.
+        # Apps from the new app template will have these; the python
+        # file check will ensure we skip South ones.
+        models_module = cache.get_app(app_label)
+        migrations_import_path = "%s.migrations" % models_module.__package__
+        try:
+            migrations_module = importlib.import_module(migrations_import_path)
+        except ImportError:
+            return False
+        else:
+            filenames = os.listdir(os.path.dirname(migrations_module.__file__))
+            return not any(x.endswith(".py") for x in filenames if x != "__init__.py")
 
     def ask_not_null_addition(self, field_name, model_name):
         "Adding a NOT NULL field to a model"