list collisions when processing the background color of a table.
This is effectively #146 Part 3c to go along with the other 2 there.
This resolves#1308.
list items.
This patch does the following things:
1. Creates nsDisplayTableBorderCollapse that draws all collapse border
of tables.
2. Stops the use of nsDisplayTableBorderBackground.
3. Lets column and column group frames generate display items.
4. When traversing the table, also traverses the column and column group
frames.
5. For each type of table frame (col group, col, row group, row and
cell), draws their own background.
