Because discoverMedata may change the portal_type of ingested Event.
* Get the last event according creation_date
* It has been decided to no hide portal_type added in Subject or in Body parts of message.
  getTitle() == 'Visit:Company A' even if 'Visit:' is a keyword to help contribution_tool
  to Construct Visit portal_type during ingestion process.


git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@41493 20353a03-c40f-0410-a6d1-a30d3c3de9de