small cleanups in threads

misago/threads/migrations/0001_initial.py

@@ -123,7 +123,7 @@ class Migration(migrations.Migration):
         migrations.AddField(
             model_name='thread',
             name='participants',
-            field=models.ManyToManyField(related_name='private_thread_set', through='misago_threads.ThreadParticipant', through_fields=('thread', 'user'), to=settings.AUTH_USER_MODEL),
+            field=models.ManyToManyField(related_name='privatethread_set', through='misago_threads.ThreadParticipant', to=settings.AUTH_USER_MODEL),
             preserve_default=True,
         ),
         CreatePartialIndex(

misago/threads/models/attachment.py

@@ -25,7 +25,7 @@ def upload_to(instance, filename):
         if filename_lowered.endswith(extension):
             break
 
-    filename_clean = u'.'.join((
+    filename_clean = '.'.join((
         slugify(filename[:(len(extension) + 1) * -1])[:16],
         extension
     ))