Respect max notification count for logging notifications.

Use a Q query to identify users for logging notifications. Should be much faster.
http://stackoverflow.com/questions/378303/how-to-get-a-list-of-all-users-with-a-specific-permission-group-in-django

Closes #576

notifications/__init__.py

@@ -9,7 +9,7 @@ MAX_NOTIFICATIONS = 50
 def notify(user, title, message=None, level='info'):
     from .models import Notification
     if Notification.objects.filter(user=user).count() > MAX_NOTIFICATIONS:
-        for n in Notification.objects.filter(user=user)[MAX_NOTIFICATIONS:]:
+        for n in Notification.objects.filter(user=user)[MAX_NOTIFICATIONS-1:]:
             n.delete()
     notif = Notification()
     notif.user = user

notifications/handlers.py

@@ -6,17 +6,27 @@ logger = logging.getLogger(__name__)
 
 class NotificationHandler(logging.Handler):
     def emit(self, record):
-        from django.contrib.auth.models import User
+        from django.contrib.auth.models import User, Permission
+        from django.db.models import Q
+        from notifications import notify
         from notifications.models import Notification
-        for user in User.objects.all():
-            if user.has_perm('auth.logging_notifications'):
-                notif = Notification()
-                notif.user = user
-                notif.title = "%s [%s:%s]" % (record.levelname, record.funcName, record.lineno)
-                notif.level = str([item[0] for item in Notification.LEVEL_CHOICES if item[1] == record.levelname][0])
+
+        try:
+            perm = Permission.objects.get(codename="logging_notifications")
+
             message = record.getMessage()
             if record.exc_text:
                 message += "\n\n"
                 message = message + record.exc_text
-                notif.message = message
-                notif.save()
+
+            users = User.objects.filter(Q(groups__permissions=perm) | Q(user_permissions=perm) | Q(is_superuser=True)).distinct()
+
+            for user in users:
+                notify(
+                    user,
+                    "%s [%s:%s]" % (record.levelname, record.funcName, record.lineno),
+                    level = str([item[0] for item in Notification.LEVEL_CHOICES if item[1] == record.levelname][0]),
+                    message = message
+                )
+        except Permission.DoesNotExist:
+            pass