[FIXED JENKINS-12061]

I still don't fully understand why the right border gets cropped, but
playing with DOM manipulation window, it seems like the cell-level
"border-right: none" is winning over the table level "border: 1px solid
talks about the border conflict resolution specified in
http://www.w3.org/TR/CSS2/tables.html#border-conflict-resolution

What this fix does is to set the cell-level right border for pane
tables. I realize that this might break table nesting inside another
table.