- implies removing the global dict used in ActivityBuffer to avoid duplicated activity insertion.
 - implies that ActivityBuffer is boud to a thread (because of get_ident) and not to a connection any more (because volatile is bound to a connection), so persistent objects must not be held outside transaction scope (the maximum scope at which a connection is bound to a thread)
   - implies modifying hook registration so that portal_activities is passed as a parameter to tpc_prepare
     - implies overloading partially TM._register method to take activity_tool as a parameter


git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@17102 20353a03-c40f-0410-a6d1-a30d3c3de9de