Fix poor performance, Implement a dummy cache of relevant_paragraph list
refactor getParagraphItem to not try/except too much without need.
Added few log entries for errors.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk/utils@41666 20353a03-c40f-0410-a6d1-a30d3c3de9de