Pass list of Message objects instead of a list of (uid, message, priority).
Store the fetched line on the Message object to retrieve the priority.

In the future, if we allow executed activity to access its related Message
object, it could also get the SQL line.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@32875 20353a03-c40f-0410-a6d1-a30d3c3de9de