- findEffectiveSpecialiseValueList was not using Breadth First Search like
  findSpecialiseValueList. Now both code have the same behaviour
- findEffectiveSpecialiseValueList was not really using effective model, not
  it use it, and if no effective model are found, an empty list is returned
- in case where no effective model are found, getEffectiveModel return None
  (instead of self). If getEffectiveModel is call with None stop_date and
  start_date, self is return


git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@28044 20353a03-c40f-0410-a6d1-a30d3c3de9de