Fix activity logs for non primary DBs (mount-points).

src/ZODB/Connection.py

@@ -312,6 +312,9 @@ class Connection(ExportImport, object):
                 # get back here.
         else:
             self._opened = None
+            am = self._db._activity_monitor
+            if am is not None:
+                am.closedConnection(self)
 
     def db(self):
         """Returns a handle to the database this connection belongs to."""