The float code was old and did not support most of CSS 2.1. So unifying
the two paths both simplifies code and improves functionality.
Improves the Reddit sidebar.
wrapper around them.
Fixes Wikipedia tables leaking out.
Along the way, I refactored tables' width calculation significantly.
This was necessary in order to properly handle floated tables, as some
of the logic had to be ported over from block flows.
When calculating the preferred width for a block, accumulate
the left and right float widths of children separately, which
is then max'ed with the normal flow widths later on.
Ref bug #2554 - improves the layout of the top bar.
