Factor out most of the database connection into db/open.py

I needed to split the db connection/opening into open.py,
due to an import loop:
- util.py needs db/util.py:ObjectId
- db/util.py would need db/models.py
- db/models.py needs util.py:slugify

mediagoblin/db/open.py

@@ -0,0 +1,37 @@
+# GNU MediaGoblin -- federated, autonomous media hosting
+# Copyright (C) 2011 Free Software Foundation, Inc
+#
+# This program 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.
+#
+# This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import mongokit
+from paste.deploy.converters import asint
+from mediagoblin.db import models
+
+
+def connect_database_from_config(app_config):
+    """Connect to the main database, take config from app_config"""
+    port = app_config.get('db_port')
+    if port:
+        port = asint(port)
+    connection = mongokit.Connection(
+        app_config.get('db_host'), port)
+    return connection
+
+def setup_connection_and_db_from_config(app_config):
+    connection = connect_database_from_config(app_config)
+    database_path = app_config.get('db_name', 'mediagoblin')
+    db = connection[database_path]
+    models.register_models(connection)
+    # Could configure indexes here on db
+    return (connection, db)