Load user model in backends

Because django1.7 can't load user model in model they way it is loaded here.

django_cas/backends.py

@@ -5,12 +5,19 @@
 
 from django.conf import settings
 from django.core.exceptions import ObjectDoesNotExist
-from django_cas.models import User, Tgt, PgtIOU
+from django_cas.models import Tgt, PgtIOU
 from django_cas import CAS
 
 __all__ = ['CASBackend']
 
 
+try:
+    from django.contrib.auth import get_user_model
+except ImportError:
+    from django.contrib.auth.models import User
+else:
+    User = get_user_model()
+
 
 def _verify_cas1(ticket, service):
     """Verifies CAS 1.0 authentication ticket.
@@ -108,7 +115,7 @@ def verify_proxy_ticket(ticket, service):
             return None
     finally:
         page.close()
-    
+
 
 _PROTOCOLS = {'1': _verify_cas1, '2': _verify_cas2}
 
@@ -148,4 +155,3 @@ def get_user(self, user_id):
             return User.objects.get(pk=user_id)
         except User.DoesNotExist:
             return None
-

django_cas/models.py

@@ -8,12 +8,6 @@
 from django.db.models.signals import post_save
 from datetime import datetime, timedelta
 from django_cas import CAS
-try:
-    from django.contrib.auth import get_user_model
-except ImportError:
-    from django.contrib.auth.models import User
-else:
-    User = get_user_model()
 
 
 class Tgt(models.Model):
@@ -67,7 +61,7 @@ def get_tgt_for(user):
         raise CasTicketException("no ticket found for user " + user.username)
 
 def delete_old_tickets(**kwargs):
-    """ Delete tickets if they are over 2 days old 
+    """ Delete tickets if they are over 2 days old
         kwargs = ['raw', 'signal', 'instance', 'sender', 'created']
     """
     sender = kwargs.get('sender', None)