Call pure transformation in an activity rather than execute in current...

Call pure transformation in an activity rather than execute in current transaction. This way we split ingestion part from transformation part.
Note: this commit will serialize argument_list to activity's mysql table in case of big packets this can be slow, in case of small appends it can be acceptable.
Instead we should call with start and end offset only and data should be read from Data Stream itself (WIP).

bt5/erp5_wendelin/WorkflowTemplateItem/portal_workflow/data_stream_interaction_workflow/scripts/DataStream_appendData.xml

@@ -58,7 +58,10 @@ argument_list = state_change[\'kwargs\'][\'workflow_method_args\']\n
 \n
 # call you own script to handle newly appended data which \n
 # is not processed yet\n
-data_stream.DataStream_transformTail(*argument_list)\n
+# Note: this will serialize argument_list to activity\'s mysql table\n
+# in case of big packets this can be slow, in =case of small appends it can be \n
+# acceptable.\n
+data_stream.activate().DataStream_transformTail(*argument_list)\n
 </string> </value>
         </item>
         <item>
@@ -72,4 +75,4 @@ data_stream.DataStream_transformTail(*argument_list)\n
       </dictionary>
     </pickle>
   </record>
-</ZopeData>
\ No newline at end of file
+</ZopeData>