[#3229] Dispose of the SQLAlchemy session after each request

This was also done on the Pylons BaseController, and it's necessary to
avoid the dreaded DetachedInstanceError during tests

ckan/config/middleware/flask_app.py

@@ -20,6 +20,7 @@
 from paste.deploy.converters import asbool
 from fanstatic import Fanstatic
 
+import ckan.model as model
 from ckan.lib import helpers
 from ckan.lib import jinja_extensions
 from ckan.common import config, g, request, ungettext
@@ -127,6 +128,10 @@ def ckan_before_request():
 
     @app.after_request
     def ckan_after_request(response):
+
+        # Dispose of the SQLALchemy session
+        model.Session.remove()
+
         # Check session cookie
         response = check_session_cookie(response)