work on project duration see #4562


git-svn-id: https://forge.indepnet.net/svn/glpi/trunk@21968 35612d4c-9d10-0410-837c-bf9dd1be60d7
more work for #4562


git-svn-id: https://forge.indepnet.net/svn/glpi/trunk@21969 35612d4c-9d10-0410-837c-bf9dd1be60d7