Add config extension, to record data changes if so configured.

setup.py

@@ -151,8 +151,14 @@ setup(
     zip_safe = False,
 
     entry_points = {
+
         'paste.app_factory': [
             'main = tailbone.app:main',
-            ],
-        },
-    )
+        ],
+
+        'rattail.config.extensions': [
+            'tailbone = tailbone.config:ConfigExtension',
+        ],
+
+    },
+)

tailbone/config.py

@@ -0,0 +1,45 @@
+# -*- coding: utf-8 -*-
+################################################################################
+#
+#  Rattail -- Retail Software Framework
+#  Copyright © 2010-2015 Lance Edgar
+#
+#  This file is part of Rattail.
+#
+#  Rattail is free software: you can redistribute it and/or modify it under the
+#  terms of the GNU Affero General Public License as published by the Free
+#  Software Foundation, either version 3 of the License, or (at your option)
+#  any later version.
+#
+#  Rattail is distributed in the hope that it will be useful, but WITHOUT ANY
+#  WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+#  FOR A PARTICULAR PURPOSE.  See the GNU Affero General Public License for
+#  more details.
+#
+#  You should have received a copy of the GNU Affero General Public License
+#  along with Rattail.  If not, see <http://www.gnu.org/licenses/>.
+#
+################################################################################
+"""
+Rattail config extension for Tailbone
+"""
+
+from __future__ import unicode_literals, absolute_import
+
+from rattail.config import ConfigExtension as BaseExtension
+from rattail.db.config import configure_session
+
+from tailbone.db import Session
+
+
+class ConfigExtension(BaseExtension):
+    """
+    Rattail config extension for Tailbone.  Does the following:
+
+     * Configures the main Tailbone database session so that it records
+       changes, if the config file so dictates.
+    """
+    key = 'tailbone'
+
+    def configure(self, config):
+        configure_session(config, Session)