Fixed error during on-the-fly edition. When you edit one object, the size of block increase wrongly because border was added as a part of size. So 2 pixels was added every edition.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@20492 20353a03-c40f-0410-a6d1-a30d3c3de9de