When deleting media that has comments and those comments have CommentNotification models, it seems to raise an error for those users. I can reproduce this by:

1. Create two users I'll call them "Chris" and "Tsyesika"
2. As Chris post an image
3. Login as Tsyesika and post a comment on said image
4. Make Tsyesika admin
5. Delete the image
6. Try to login as Chris

Those steps should trigger this exception:

Error - <class 'jinja2.exceptions.UndefinedError'>: 'mediagoblin.db.models.Graveyard object' has no attribute 'get_reply_to'
URL: https://dev.tsyesika.se/
File '/home/tsyesika/mediagoblin/lib/python2.7/site-packages/Paste-1.7.5.1-py2.7.egg/paste/exceptions/errormiddleware.py', line 144 in __call__
  app_iter = self.application(environ, sr_checker)
File '/home/tsyesika/mediagoblin/mediagoblin/app.py', line 342 in __call__
  return self.call_backend(environ, start_response)
File '/home/tsyesika/mediagoblin/lib/python2.7/site-packages/werkzeug/wsgi.py', line 591 in __call__
  return self.app(environ, start_response)
File '/home/tsyesika/mediagoblin/mediagoblin/app.py', line 276 in call_backend
  return self._finish_call_backend(request, environ, start_response)
File '/home/tsyesika/mediagoblin/mediagoblin/app.py', line 318 in _finish_call_backend
  response = controller(request)
File '/home/tsyesika/mediagoblin/mediagoblin/views.py', line 46 in root_view
  return view(request)
File '/home/tsyesika/mediagoblin/mediagoblin/decorators.py', line 47 in wrapper
  return controller(request, *args, **kwargs)
File '/home/tsyesika/mediagoblin/mediagoblin/decorators.py', line 170 in wrapper
  return controller(request, page=page, *args, **kwargs)
File '/home/tsyesika/mediagoblin/mediagoblin/views.py', line 37 in default_root_view
  'pagination': pagination})
File '/home/tsyesika/mediagoblin/mediagoblin/tools/response.py', line 36 in render_to_response
  render_template(request, template, context),
File '/home/tsyesika/mediagoblin/mediagoblin/tools/template.py', line 144 in render_template
  rendered = template.render(context)
File '/home/tsyesika/mediagoblin/lib/python2.7/site-packages/Jinja2-2.8-py2.7.egg/jinja2/environment.py', line 989 in render
  return self.environment.handle_exception(exc_info, True)
File '/home/tsyesika/mediagoblin/lib/python2.7/site-packages/Jinja2-2.8-py2.7.egg/jinja2/environment.py', line 754 in handle_exception
  reraise(exc_type, exc_value, tb)
File '/home/tsyesika/mediagoblin/mediagoblin/templates/mediagoblin/root.html', line 22 in top-level template code
  {% set feed_url = request.urlgen('mediagoblin.listings.atom_feed') %}
File '/home/tsyesika/mediagoblin/mediagoblin/templates/mediagoblin/base.html', line 67 in top-level template code
  {% block mediagoblin_body %}
File '/home/tsyesika/mediagoblin/mediagoblin/templates/mediagoblin/base.html', line 69 in block "mediagoblin_body"
  {% block mediagoblin_header %}
File '/home/tsyesika/mediagoblin/mediagoblin/templates/mediagoblin/base.html', line 183 in block "mediagoblin_header"
  {% include 'mediagoblin/fragments/header_notifications.html' %}
File '/home/tsyesika/mediagoblin/mediagoblin/templates/mediagoblin/fragments/header_notifications.html', line 9 in top-level template code
  {% set media = comment.get_reply_to() %}
UndefinedError: 'mediagoblin.db.models.Graveyard object' has no attribute 'get_reply_to'

When you setup Mediagoblin for the first time and use postgres for some reason you get an exception claiming the Graveyard table doesn't exist. I suspect it's somehow related to the switch to alembic however i'm unsure.

Steps to reproduce:

1. Follow basic instructions: ./bootstrap && ./configure && make
2. Setup a brand new postgres database (configure to use it in mediagoblin.ini)
3. Run the ./bin/gmg dbupdate

I noticed when debugging #5391 that migrations were forced to use SQLite which was defined in alembic.ini. I've pushed a fix for this which sets that option based on mediagoblin.ini however we shouldn't need to do this. We're providing a session on the manager which seems to be completely ignored, this leads to misleading code.

We need to decide between these two options:

1. We remove the session from AlembicMigrationManager to make it obvious alembic will internally open a new one
2. We make it so Alembic uses our database connection/session we've provided so it doesn't open another.

The way the code looks having a database connection we've setup but (seemingly) not using it is misleading and probably why it wasn't spotted earlier.