Before issue #146, border-radius on row groups, rows, column groups, or columns don't apply to the background of each cell, yet the border-radius on the cell itself does.
After issue #146, the behaviors changed. In this patch, I tried to revert the behaviors of border-radius on table row groups, rows, column groups, or columns back to what happened before issue #146.
Also: Don't override GetBorderRadii in nsBCTableCellFrame.
