Fix bulk delete of batch rows.

Actually I didn't see this fail, but I've seen one instance where someone
else did.  This should hopefully be a safe approach.

tailbone/views/batch.py

@@ -874,7 +874,7 @@ class BatchRowGrid(BaseGrid):
         """
         Delete all rows matching the current row grid view query.
         """
-        self.query().delete()
+        self.query().delete(synchronize_session=False)
         return HTTPFound(location=self.request.route_url(
                 '{0}.view'.format(self.route_prefix),
                 uuid=self.request.matchdict['uuid']))