update an specified selection only in firstPage() and lastPage(), because modifying REQUEST will affect all listbox in the page. this will fix the failure in testPagerInViewMode of erp5_ui_test.


git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@28536 20353a03-c40f-0410-a6d1-a30d3c3de9de