This improves automatic table layout for wikipedia.

It's far from a complete implementation of automatic table layout.

The CSS 2.1 spec simply says: extra space should be distributed between cells.

Previously we would divide this up evenly between each cell.

This patch changes the behaviour slightly so that:

If there is extra space, AND
Some cells are at their preferred width, AND
Some cells are not, THEN
    Distribute the space evenly among the cells that are not already at their preferred width.

There needs to be a much more complete implementation of auto table layout to make tables work in all situations.