managers: fix the for_tag() method

the Q object is not in the django.db.models package

django_journal/managers.py

@@ -1,10 +1,9 @@
 from django.contrib.contenttypes.models import ContentType
 from django.db.models.query import QuerySet
+from django.db.models import Q
 from django.core.cache import cache
 from model_utils.managers import PassThroughManager
 
-import models
-
 
 JOURNAL_METADATA_CACHE_TIMEOUT = 3600
 
@@ -70,6 +69,8 @@ class JournalQuerySet(QuerySet):
         '''Returns Journal records linked to this tag by their own tag or
            the tag on their data records.
         '''
+        from . import models
+
         if not isinstance(tag, models.Tag):
             try:
                 tag = models.Tag.objects.get_cached(name=tag)
@@ -77,9 +78,9 @@ class JournalQuerySet(QuerySet):
                 return self.none()
         # always remember: multiple join (OR in WHERE) produces duplicate
         # lines ! Use .distinct() for safety.
-        return self.filter(models.Q(tag=tag)|
-                models.Q(objectdata__tag=tag)|
-                models.Q(stringdata__tag=tag)) \
+        return self.filter(Q(tag=tag)|
+                Q(objectdata__tag=tag)|
+                Q(stringdata__tag=tag)) \
                 .distinct()