Fix/better user model determination (#435)

* convert user model determination to proper function call

* remove unnecessary checks

Author: seawolf42

simple_history/models.py

@@ -8,6 +8,7 @@
 from django.apps import apps
 from django.conf import settings
 from django.contrib import admin
+from django.contrib.auth import get_user_model
 from django.db import models, router
 from django.db.models import Q
 from django.db.models.fields.proxy import OrderWrt
@@ -25,6 +26,7 @@
     post_create_historical_record,
 )
 
+User = get_user_model()
 registered_models = {}
 
 
@@ -216,9 +218,7 @@ def copy_fields(self, model):
     def get_extra_fields(self, model, fields):
         """Return dict of extra fields added to the historical record model"""
 
-        user_model = self.user_model or getattr(
-            settings, 'AUTH_USER_MODEL', 'auth.User'
-        )
+        user_model = self.user_model or User
 
         def revert_url(self):
             """URL for this change in the default admin site."""

simple_history/tests/tests/test_manager.py

@@ -1,19 +1,16 @@
 from datetime import datetime, timedelta
 from operator import attrgetter
 
+from django.contrib.auth import get_user_model
 from django.db import IntegrityError
 from django.test import TestCase, skipUnlessDBFeature
 
-try:
-    from django.contrib.auth import get_user_model
-except ImportError:
-    from django.contrib.auth.models import User
-else:
-    User = get_user_model()
-
 from ..models import Document, Poll
 
 
+User = get_user_model()
+
+
 class AsOfTest(TestCase):
     model = Document