4.0: merged (by hand) changeset r2585 from trunk (sets natural prior...

4.0: merged (by hand) changeset r2585 from trunk (sets natural prior boundaries when optiosn_.prior_trunc == 0)

git-svn-id: https://www.dynare.org/svn/dynare/branches/4.0@2586 ac1d8469-bf42-47a9-8791-bf33cf982152